You can get a great combo for your budget!
$60.90 BIOSTAR M7NCG-400 (Nforce 2 IGP)
$84 AMD XP 2600+ (Includes cooling fan)
$84 Kingston PC3200 2x 256MB
Total $228
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edit: For your cousin's use though, CPU speed is not that important, nor is the integrated GF4 MX of the NF2 IGP. Something like this will do fine. 256MB is the minimum amount of ram you want to have, but 512MB is recommended if running Windows XP for better performance. Try to go with PC3200 ram because it costs only a little more compared to it's PC2700 and PC2100 counterparts and will hold up much better in the future.
$46.2 BIOSTAR M7VIG PRO (KM266 IGP SDR/DDR)
$47 AMD XP 1500+ (Includes cooling fan)
$43.59 CORSAIR PC3200 256MB
Total $136.79
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Biostar makes great boards. Have had no problems with them. Friend has been running Biostar NF2 IGP on his lan box for a year now. And cousin has been using the Biostar KM266 for 1.5 yrs. Stable, and quick.
Mwave is a reputable online store. So is Newegg. Check
reseller ratings before buying anywhere.