32bit Windows is a little quirky in the memory management department. It has a hard limit of 4GB, but things don't work quite that way in practice. PCI devices use the last 1GB of the four for address space. And from there it gets worse. If you f.x. install a graphics card with 1GB RAM, Windows will subtract that 1GB from your total memory pool. That's only 3GB in size. In practice you'll end up with 2GB usable RAM. So in practice adding more RAM is marginal at best...
so the DDR3 or 2 makes no difference with my old system?