I doubt your problems are due to the processor, and although memory might be a factor it isn't the only one - rebooting is sually a video issue, so the first thing to check is that you have the latest drivers.

Under XP Home no application can address more than 2GB of RAM, though the system can address up to 4GB and use the excess for itself or for other applications. Some applications can, under XP Pro, address up to 3GB of RAm but D|S isn't one of them. Although XP can go up to 4GB, the upper part of the space is already used by components such as the video card and you are not likely to get more than 3GB of usable RAM however much you add - but up to 3 may be useful, 2 isn't the cut-off.

A dual core chip will help when rendering with 3Delight, but not with scene creation as D|S itself is single-threaded (beyond the fact that other things can run on the second core, reducing competition).