I found the "cpu support" section for your board on foxconn's website. Your board chipset is too old for newer core2 duo cpus; the fastest it supports is the 516 P4. Starmicro is a good vender for older cpus. They have the 515 p4 for $33.
O1die's right, p4 516 is the fastest supported. But really, you will have almost no performance gain due to this change, you have to replace your mobo too. Look for some used ones if you do not have much cash. You can look for some combos like mobo+cpu and memory. Ask us before you purchase, I'd say that cheap c2d or pentium dc is gonna do fine for you.