How to choose the computer memory that is right for me?
More memory (ram) is always a good thing. Depending on the make / model of your computer, it'll be different - eg, SDRAM, DRAM, and then the speed / eg, 233 mgz or 266 mgz etc.
Check your computer paperwork or visit the manufacturer's web site to figure out the exact memory you should buy for it.
http://www.crucial.com has a great "Memory Advisor Tool" on their homepage that tells you what type of RAM your computer uses. Of course, you can purchase the RAM wherever you want - but this will at least tell you what you need.