Don't think they make PC2 3200, that'd be DDR2 400. If it's PC 3200, then that's DDR memory, and no you can't put DDR2 into a DDR machine.
Since it's Dell, it's most likely PC2 4200, which is DDR2 533. Dell loves to put s*** RAM in their machines. Chances are, the motherboard is also s***, and only supports DDR2 533/667. If my hunch is correct, then any DDR2 800 memory put into that machine would be downclocked to DDR2 667. And since it's a name-brand computer, you cannot overclock through the BIOS so you're stuck at those speeds. It will definitely fit and work though, and since DDR2 800 is so cheap, I'd get it anyway if you're adding more memory to the system as it's usually higher quality. I wouldn't replace a 2x1GB set of DDR2 533 with a 2x1GB set of DDR2 800 in a Dell though, just not worth it since it will probably run at DDR2 667 anyway which isn't much improvement. Don't worry, it will die soon enough and you can replace it then
lol. My Dell memory lasted 3 years.