Funny thing......... I just did a similar upgrade for a customer, but with a Twist !
He wanted a 512mb PC133 RAM module added. No probs I thought, then I found it cost the same as a new 2200+ Sempron with a new Asus mainboard.
He then only had to fork extra out for a cheap PC3200 512mb RAM stick.
He now has a PC that's 3 times faster for just a few dollars more ..... because I wouldn't let him upgrade with old junk!