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#11
Unless it is identical to the 2 GB kit, you never know for sure if it will play nice or not. Go for it, and if it doesn't, sell the 2 GB and run with the 4 GB kit for now.
leave the 2 gigs in. Make sure you find out what you have first. you can download either everest, or cpu-z to tell you really detailed info abt the ram. with that in hand you want to get the exact same specs on the 4gig kit you buy
Ken
Tom
Just a little further clarification: if you want 4G, buy a 2x2G matched pair (as an example only look here: Newegg.com - Crucial 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 667 (PC2 5300) Dual Channel Kit Desktop Memory Model CT2KIT25664AA667 - Desktop Memory)
As explained, the matched pair Dual Channel Kit will guarantees that they work well and according to the specs (not according to the lowest spec between a non-matched pair)
Hope it helps