Why not try configuration management software?
This category of software lets you manage collections of
source code... often, a developer "checks out" his/her
copy of a file; if another developer also works on the
same code, there are various mechanisms for merging the
two people's changes (depending on the package you are using).
A free solution I use often is CVS.
If you are a Windows person, there is a GUI tool called WinCVS that a lot of people like.
One point: regardless of the package you use, I'd recommend you help set up a "build and test" environment for your graphical designers. With JSP, minimizing the Java code in the page helps a lot, but non-techies still break stuff through no fault of their own, if they don't have a JSP container available to make sure their "cosmetic" changes don't cause unexpected problems.