Some things to try:
1. Basic Windows precautions help - XPsp2 Firewall,
default acct has only User rights, not Power/Admin,
etc. You can freeze a config (make it fix itself daily)
using Reborn cards from www.lenten.com or the like.
Software solutions like DeepFreeze from Faronics
are another popular way to "lock down" public PCs.
2. Use OS X with (a.) Virtual PC 7 for any apps that
just have to be Windows, (b.) one generic local
account, whose home dir is rebuilt each boot, and
(c.) OS X Server with NetBoot for fast deployment.
If you can afford Apple, OS X is very secure and
reliable "out of the box", meaning less tweaking.
3. Thin clients from www.hp.com/products/thinclients
or the like. The server will cost a bit in cash and
(unless you try the Linux Terminal Server Project)
cash, but client setups are instant. This can save
a bundle over some years and cut security issues.
