I'm looking for a proxy server to control my users' access to certain sites
on the Internet. We have about 100 users with light-medium usage. Probably
no more than 10 people at a time accessing the web. I think Border Manager
(or Access Manager now I guess) would be overkill.

I'd like to leverage our eDirectory user accounts instead of having the
users log in when they want to use the Internet. I'd like it to be seamless
and as cheap as possible. My preference would be to just trust them and send
out occasional reminders about firm policy, but administration is getting
really paranoid

Is Squid the best choice?
Can I run it on an existing Windoze server that we use for internal cost
recovery tracking?

Are there others that would be as good or better?