If you want to limit how much space each user has, then disk quotas are the way to go, however if you want to limit the size or certain folders, ie no more than 200mb in C:\Users then I dont actually know a way.
I have implemented a work around for the moment, whereby the size of the directories is reported to me via a simple VB program, allowing me to limit access if the folder gets too large.
Hopefully someone will know a more suitable solution. They say hard work never killed anyone. But dont like taking chances.