Just to make sure I was clear, I agree with the two previous posters that you *cannot* mix different *types* of memory.

ECC, DDR, and DDR2 are all unique types and cannot be mixed together. (I lost confidence in the the response from LeavingLAS when it became clear he didn't know that ECC was a special type of memory, not a feature of premium versus value brands.)

You can however, mix different brands and speeds of DDR memory, so long as each stick is rated at least as high as the speed your PC memory runs at. (PC133 vs PC100 is an exception if that's what you've got.)

I have nothing against Crucial. (In fact they supplied the four sticks of ECC for my server which requires that type of memory.) They just aren't going to be price competitive with a Circuit City loss leader special on memory close to free after rebate.

If you are adding memory to a mission critical server, I'd go with Crucial. For a laptop for a 12 year old, I think the generic brand on sale at Circuit City is fine.