I suggest using SVN, because:
- Source control gives you excellent history. You can see where what changes have been made, thus providing a great way to see what's changed over time (even better if you fill out the submit summary each time)
- To the developer, it provides an excellent fallback if something goes horribly wrong. You can revert changes to a file back to any point in its history, so you can try out that mod you wanted to make, and if it doesn't work, roll it right back easily.
- It provides a central repository that is much easier to back up than running around to different developers' computers.
- It allows you to branch a project off in a different direction - useful for specializations and customizations.
- It enables more than one developer to work together on the same project, and the same source, by letting you merge and otherwise manipulate changes to one central copy.
I suggest NOT using VSS - see this page for reasons:
http://www.highprogrammer.com/alan/windev/sourcesafe.html for more reasons.
