There's compatible RAM and there's incompatible RAM. That's one.
And there are limits on the amount and size of sticks, the combinations of sticks and the total amount of memory that your motherboard can handle. That's two.
The best thing to do: visit www.crucial.com and enter your PC's data into their memory search tool. This will give you all information you buy (or use existing) sticks.
Also interesting: what does the documentation of your Dell say about (a) what memory can be added and (b) how to do it?
http://www.bleepingcomputer.com/tutorials/tutorial122.html tells a lot more!
Kees
I ran a diagnostic report from Norton360 on my 2005 Dell Dimenion 4700 XP Home Edition 32 Bit service pack3. it has an Intel Pentium 4 CPU. The report said to add ram, I have a 256mb DDR, 512mb DDR. Can I use either one of thes and if so how would you insert. Thank You

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