Upgrade Dimension 8400 to Windows 64bit ..either Vista or 7

xales_username

1) Is this enough for my desktop to run windows 64bit either vista or 7?

4gb of DDR2 RAM should be fine.

Replace my ram with two of these "Kingston 2GB 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop

You need to check that the Dimension 8400 supports 2gb modules, both Dell's spec's and Crucial state the maximum is 1gb module per slot, total 4 x 1gb modules.

 http://www.crucial.com/store/listparts.aspx?model=Dimension%208400%20Series&Cat=RAM

2) What would be a good CPU upgrade that will run good on my motherboard?

You can upgrade to any Socket LGA775, 5xx, 6x0 or 6x2 processor, with 90nm architecture, but not the 6x1 processors.

8400 systems do not support dual core [Pentium D] or Core 2 Duo processors.

The 670 3.8Ghz is the largest.

  Prior to installing the processor, check that you have BIOS version A09, or higher, when support for newer processors was added.

3)Is any of this a good idea??

That's debatable, personally I would use the money towards, buying a used Core 2 Duo, or Core 2 Quad system.

Because the Dimension 8400 only supports single core processors, is the reason why I sold my two 8400's, 5-+ years ago.

Bev.