Yes. There should be no problem whatsoever. The PC3200 will underclock itself to PC2100. Then, when you upgrade, and put your PC3200 into a system that supports PC3200, it will run at its native speed.
Besides, PC3200 is easier to find and around the same price as slower stuff.
For more reassurance, I actually did this to a computer very similar to yours not long ago, without a single problem.
Intel E6750...........PSN: ELBATROP
XFX nForce 650i Ultra
Patriot PC2-6400 8GB (4x2GB)
36GB WD Raptor
Samsung SyncMaster 931c
Samsung SyncMaster 750s
Windows 7 Home Premium 64