You could try looking at some 800MHZ DDR2:
http://www.ebuyer.com/product/142380
If you don't mind running the RAM in single channel then get one RAM module only:
http://www.ebuyer.com/product/165306
Alternatively get 2 of these 1GB 1066MHZ DDR2 modules:
http://www.ebuyer.com/product/143020