Dell Optiplex GX280 Motherboard - What type of CPU and Memory do I need?

I purchased a G5611 Motherboard ( A guy on Ebay told me it was the correct board for my Dimension 8400 - Now it seems I find out that it's not for a Dimension at all, but an Optiplex GX280 ).  Anyway, I want to upgrade to a 3.0 Ghz processor and 1GB of RAM.  Do I need a Intel 530J processor or will a 530 work okay?  Also, can I use the same memory from a Dimension 8400 or do I need to buy new RAM?  Thanks for any and all help.