automatically enter username and password

I work for a school and we would like to track the usage habits of teenagers that user laptops in our library. Whenever they login to the laptop a new profile is created for them in XP. We can put the software rescue time into the startup for all users but how do we have the client automatically login with the account we created for this purpose. Is there a command line parameter we can pass?

Any help you could provide would be great- this will give us very valuable data on our computer and internet usage.