I have a dell dimension 8400 and i think it uses intel 925x. Not exactly sure becuase i went to a few different sites to find info. Anyways, I was wondering what processors i could upgrade it to or what would be compatible with it like quad cores or duo cores.
Also im looking to add more ram and was wondering what kind of ram i could add. I think it uses DDR SDRAM. Can I add ram like pc 6400 ddr2 dual channel rams for that?

can u give the model of the computer? as we need this to find out what the computer can accept.

Isnt Dimension 8400 the model?

We find the Dell 8400 to be a top end, but aging, Dell desktop. I doubt you will find much room for improvement of CPU in that motherboard... certainly not equal to the cost. Don't try a high end cpu unless you first replace the power supply with a high end one.
This Dell of yours can use DDR2 PC6400, with up to four modules to max out at 4 GB, but of course that version of Windows will only use 3.5 GB. All memory will run at the speed of the slowest module, and you may be limited by the FSB anyway.
I would remove all old memory, and max out the new memory at PC2 5300 or PC2 6400 and leave the cpu alone... because your FSB isn't going up much on that board.

Ok cool. Thanks alot for the help.

As RAYBAY points out ,that motherboard leaves really no room for expansion ,"well "any to really notice /big inprovements ,you never stated what do you use that computer mainly for ?now that CPUs and motherboards have came way down in price.even GPUs ,i bought my extra EVGA 8800gt for like $129.99, at tiger, so anyways you can build or get built a really cheap system now adays, mine is only about 3 months old and i pieced it together for under $1200.00 taxes in!

Yea I just wanted to upgrade it a bit so I can play some of the new games coming out like fallout 3 and some others that slip my mind at the moment. I would try to piece together a new one but i figure I could just spend less than half of what it would cost to build a new one instead.

yah you could do that too spend about 1/2 and pick up a nice MOBO/CPU combo deals,those are good deals right now !id have to check my invoice ,but if memory serves .i paid about $330.00 for the the xfx680i board<only sli,not the tri-sli one and a Q6600 BX-GO stepping one.<no fan .OEM model