OK, I need some advice/guidance as to a pretty simple problem that I am not able to solve because I havnt had time to think on my own about it.

A friend of mine wants to see if linux is a viable option for his business that is primarily internet kiosks and pay-to-use public internet access... I firmly believe it is, however, I dont know how to scale down a system or limit a systems access for it to be a viable option.

I have suggested Kde because it is the most user friendly (imho) and that is about as far as I can get.

It is a series of iMac P.O.S.s with yellowdog 2.4
they are set up as development systems cause I didnt feel like manually selecting crap.

how would i get these to be as limited as to only allow Pop mail and web browsing and as automatic a logon as possible?
any help would be appriciated. thanks