DDR3 memory is set to take over, and your computer probably takes DDR2 (read a comparison here). That isn’t bad news though. Prices on DDR2 have dropped and continue to drop, making an upgrade a good idea. You can get another two 1 GB sticks to match the ones you already have for less than 50 bucks; a lot less than 50 bucks if your existing memory isn’t particularly fast.
And we aren’t talking CheapTech Brand Corporation of No Fixed Address products either. Corsair, OCZ, Buffalo, Crucial, Kingston, and the other big names, along with their resellers, are all happy to get DDR2 out of their warehouses. Expect big discounts and look for big rebates.
The thing is, DDR2 is getting so cheap; should you just get that extra 2 gig to match your existing memory, or find another use for the existing memory (there is always eBay) and get a shiny new 4 gig kit?