SONORAN DESERT, by Peter Davies and David Robinson, Ransom Publishing, Single user Pounds 39.95 plus VAT, ISBN 1 9001 00 8, Network Pounds 99.95 plus VAT, ISBN 1 9001 01 6, Windows CD (Macintosh version planned)

Some CD-Roms are lecture substitutes. Some simulate lab work without blood, fire or biohazard. Sonoran Desert, spanning the education and consumer markets, attempts to recreate a well organised field trip or a sample of high-quality eco-tourism.

Backdrop to a thousand Western movies, the Sonoran desert of southern Arizona and northern Mexico is the land where house-high, branched saguaro cacti replace trees. Distant epochs of erosion carved out the 50-mile vistas of the basin and range country. A land of big skies which love Panavision but, predictably, are going to suffer on the small screen. That is the price of interactivity, and it is a fair exchange.

The software used is the Biodiversity shell, one of the most impressive products to emerge from the funding councils' Pounds 43 million Teaching and Learning Technology Programme. The shell itself is content-free. It is a reusable framework for multimedia productions, more closely adapted to educational use than the leading commercial packages such as Authorware Professional and Macromedia Director. It was used to create the Open University's Multimedia Brain and the TLTP biodiversity consortium's own CD - a collection of around 30 tutorials including a mini version of Sonoran Desert.

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TLTP consortia are now under pressure to commercialise their work. The biodiversity consortium, led from the University of Nottingham, has attacked the market more convincingly than most. Sonoran Desert is aimed beyond the ÖйúAƬ sector to the consumer and secondary school markets. Wisely the academics have put the marketing in the hands of a small specialist company, Ransom Publishing.

The software is easy to interact with, does not take long to learn, and usually behaves in an intuitive and predictable manner. There are a few user-interface irritations such as the excessively tiny "close" boxes on the Biodiversity shell's non-Windows windows, and the fact that you cannot ask your guide a question while taking notes in the photo album.

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The "story" is that with an expert guide and a party of fellow students or tourists, you set out from a field centre to a number of hiking stations from which you can explore the desert on foot. If you need a motive other than sheer curiosity, you can tick off species on a checklist as you find them.

The disc is designed as a learning experience, not a reference source. You can visit the field centre library and search through photographs and video clips, but it feels like cheating. The outdoors beckons, and there you will need skill and patient search to find what you are looking for, just as you would in the real desert.

Your rucksack contains various useful items including a camera. You can use these to put together a personal record of your journey.

Long distances are covered instantly in a four-wheel drive vehicle. Local explorations on foot will occupy most of your time. Short-range time travel is also catered for. Click on the moon icon and night falls. Your view of any nocturnal animal is authentically indistinct, but you may be able to get a closer look with a torch. Click on the sun icon, day instantly returns and the night creatures vanish. There is, however, no comparable device for exploring the desert's changing seasons.

Apart from the land itself, your desert guide is the chief source of knowledge. He is the guy in the cowboy hat at bottom right of the screen, gazing out into the landscape. The guide's commentary was recorded by David Robinson, who shares the author credit with Peter Davies. At first it seems strange to have a guide with an English accent, but it grows on you.

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As the guide warns, "you'll see very little unless you go looking for it, and nothing much will happen in the desert unless you make it happen." So an exploratory, inquisitive approach is essential. Search for the hotspots in each image where you can manipulate things (a hand cursor appears), or look closer (a magnifier cursor appears). Mouse clicks in other parts of the image will bend your path left or right, take you deeper into the country ahead or back the way you came.

You do have to use your head. The preliminary "desert training" is fairly directive but your guide responds with good humour if you go off in an unintended direction. Click on the figure of the guide at any time, and available questions appear on a menu.

This is how you find out, for example, that washing clothes in tomato juice may help to remove the odour of skunk.

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Video (from the BBC Natural History Unit) is used sparingly, for the animal subjects which most deserve it. Audio, however, is abundant. Much of the information comes spoken by your guide. Do ask him questions. You will find out more than by just listening to his comments as you move around the countryside and examine the plants and animals. If you are hard of hearing, dislike the narrator's voice, or want to avoid disturbing other people in the room, you can turn the volume down and have the commentary displayed as text.

Apart from the majestic landscape itself, it is the plants that give the cactus desert its unique look and smell. (They also provide unusual habitats for animals such as the cactus wren.) However, the disc is a little disappointing for the plant-lover.

The checklist of a couple of dozen plant species and genera includes the striking common species (saguaro, barrel and hedgehog cacti, cholla and prickly pear, ocotillo, palo verde) and a selection of other flora including the desert's greatest vegetable oddity, the boojum tree with its plump moisture-conserving trunk.

Wisely the disc refers to species by their common English or Spanish names, but the Latin names are also provided.

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Animals are better represented than plants. Birds and mammals with their high-performance physiology have found many unlikely ways of surviving in the desert. As always, it is a surprise to be reminded how many amphibian species live in arid environments. But the animal stars of the desert are the reptiles and invertebrates. Some recent CD and television productions have exploited nature's "nasties" to the limit. Sonoran Desert gives the spiders, snakes and scorpions a more balanced treatment. But the rattlesnake swallowing the squirrel is not for delicate stomachs.