Hi there
A few things you should know before you even start.
In recent years there have been 3 diffrent RAM types for laptops, and they cannot be swapped. The 3 kinds are RD, DDR and DDR2. so make sure you know which one you need.
Another important thing, is the RAM limit of your comuter. Some farely new laptops can only work with 1 GB, and if you plan to buy 1 GB, you will probobly want to have more than that (since you already have 256 or 512 MB). You should check the manufecturer's website to make sure.
one more thing before I get to places you can buy at - some RAM chips are designed specifcly for a certian brand of laptops (Kingston for examples creates DDR2 chips specifcly for IBM, HP and other companies).
If after all that, you still want to buy a used RAM chip - here are your options:
1. www.homeless.co.il
2. www.yad2.co.il
3. used parts dealers - if you want phone numbers - let me know.
Good luck