junkeymonkey :
that chip is not on the supported cpu list is it ??? [ Phenom II B55 ] best stick to what asus shows as tested and supported
meant to down vote that but goofed it .. sorry
I guess that means you have no experience with AM2+/AM3 CPU's? Here I will explain something to you that your not going to get from just reading a list, it comes from actually using the hardware. A good deal of Athlons, Semprons and Phenoms are unlockable to something else you just have to know what they are, I have a nice long list saved should you want to look.
B Series are Business Class Phenoms crippled to a Dual Core and most will unlock perfectly fine, some are rejects but the majority are not. Phenom II X2 555 and B55 are coded the same just not labeled, any Bios that supports a X2 555 will take a B series. If you unlock a Phenom II X2 555 it will show as a B55 X4.
OP I will warn you on the RAM avoid using difference brands and try to keep it Crucial, GSkill, Kingston, Kingsmax, Geil, Qimonda, Samsung. Nothing is more frustrating that having the computer pick or not pick up your RAM every time you turn the thing on. DDR2 1066mhz is pretty expensive in 2GB sticks Look on Ebay or Classifieds to find a reasonable price. $75+ for a CPU and $75+ for RAM for a PC this old doesn't seem like a good investment.