it the current moment now but within the next 6-12 months dual core will be huge as more games will support it and more applications. Plus when the CPU prices drop for the 939's it will make for a very cheap upgrade.
If you go to an intel dual core, you'll need a new proc, mobo, and ram (DDR2). I would just go with a 165, and OC it to FX-60 speeds. Might take some luck to get that high, but you should get to at least 4800 speeds (2.4)