If you provided a budget for us, we could provide far more acurate advice.

In general, judging by what's been said so far, you're looking at something like an Intel Core 2 Duo E6300/E6400 with 2GB of RAM. The best budget motherboard is the Gigabyte GA965-DS3. Stay away from brands like Asrock, they generally make the worst motherboards on the market.

And build it yourself, because it's not hard at all, it's far cheaper and like others have said, you'll learn something new.