Hi vicson,
If your project is not Open Source, there are a number of options. Git is a good decentralized source control system, which doesn't require a server - each working tree is also a complete repository. You can use any HTTP or SSH server as a repository you can all synchronize to, or you can synchronize between local or network filesystems. The Git Tutorial is a good introduction to git:
http://www.kernel.org/pub/software/scm/git/docs/v1.2.6/tutorial.html
If you want somewhere centralized to host your repository, there are a number of services. Nearly all of them charge at least a nominal amount if your project is not open source. I personally recommend
github.com - their basic account for private repositories is $7/month for 5 private repositories and 1 collaborator, going up to $12 a month for 5 collaborators.
Note that my recommendation of github is an entirely personal one, and shouldn't be construed as any sort of official support for it. :)
-Nick Johnson
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Nick Johnson, Developer Programs Engineer, App Engine