Commissioning a museum computer exhibit can be a confusing business. This page has links to documents written by a range of experts. At the moment a lot of this advice is from people I know. But if you know of some other good advice on the web let me know and I'll add a link.
Home page of the Tate Modern handheld computer tour. Explains the system, gives you a taster and some of the evaluation and research done during its development. A great resource and an example other institutions should follow.
John Benfield is New Media Manager at the Natural History Museum in London. He's written a set of guidelines for making museum kiosks accessible.
Gail Durbin describes the how the V & A museum in London used computer exhibits to facilitate learning. This paper goes through the whole process from analysis of visitors' needs, different types of exhibit and surveys on their effectiveness.
The British Interactive group brings together many people in the UK who develop interactive exhibits. Although their website is mainly concerned with mechanical exhibits there's a lot of good general advice.