Hi all, First post from a computer idiot. I recently bought a new PC, cheapest I could find at the time (Dell Dimension C521) which came with only 256MB of RAM. It's running slower than my previous PC which had 256 + 128mb so I'm assuming it's the lack of RAM as the rest seems higher spec. So I'm looking to add some RAM by the cheapest route possible and I've been looking at ebay, I'm not planning on adding much as I'm on a very, very limited budget so probably just doubling it. My new PC takes DDR2 so my old memory is no use. My questions are: 1)I need matched pairs to add, but can I add a pair to the one already fitted? 2)My manual says it supports 533Mhz, 667Mhz & 800Mhz so is the 400Mhz pair I've spotted on ebay no use? Are there any other issues I need to be aware of? I think thats it. Cheers.