I usually reply within 24 hours - you only waited 17 hours before commenting that no-one had replied.
The two ways I know of are using Microsoft Visual Source Safe, which comes with Visual Studio, I think. This lets you share source - I'm not sure if it works over the Internet, you would have to try that.
The other way is with CVS (concurrent versioning system) which is an open source solution that is widely used in the Unix community. I am using it myself to control my development, eg., MUSHclient versions.
You can use CVS from Windows, as I am doing, but as far as I know the server (where the data actually resides) needs to be on a Unix box (eg. Linux, OpenBSD, FreeBSD etc.)
If you have a spare 486 or low-end Pentium you could set one up using Linux/BSD to act as a CVS server, and then install the Windows CVS client on the developers PCs.
Read more about CVS at http://www.cvshome.org/
One of the nice things about CVS is it lets multiple developers work on the *same* source at the same time (not the same lines of course) and then merges all their changes together when they are ready. I don't think Source Safe does that.
If you are trying to set up automated builds and or nightly builds check out this tool. I found it easy to set up and it has support for mulitple projects as well as interproject dependencies.
From Anthill website:
"Anthill is a tool that ensures a controlled build process and promotes the sharing of knowledge within an organization. Anthill performs a checkout from the source repository of the latest version of a project before every build and tags the repository with a unique build number after every build. It supports many reposistory adapters including: CVS (Concurrent Versions System), Visual Source Safe, Perforce, PVCS, StarTeam, MKSIntegrity and FileSystem. Anthill also automatically updates a project intranet site with artifacts from the latest build. Anthill is an extension to the Apache-Ant project and is compatible with version 1.3, 1.4 and 1.5 of Ant. Anthill is Open Source and is released under a Mozilla-like license."