I'm not planning to run skyrim on this, but the community here has always been very knowledgeable.
The online documentation wasn't clear on how much RAM the motherboard supports. I was wondering if I could upgraded to 4 GB. It's a cheap machine that has two RAM slots. I was hoping to use 2GB PC5300 DDR2 667MHZ 240PIN ECC Reg 2X2GB RAM or any other 2x2gb that would down clock. It all comes down to can it support 2 GB sticks.

Suggests that it can take 4 GB
http://megamemory.com.au/20-transcend-jetram-4gb-pc6400-ddr2-800mhz-2x2gb-non-ecc.html

Yet another site says 2 GB max
http://www.memorystock.com/ram/eMachinesW3653RAM.html

Hardware reference Guide
http://www.helpowl.com/manuals/eMachines/W3653/67250

Motherboard specs
http://www.e4allupgraders.info/dir1/motherboards/socket775/ecs945GCT-M3.shtml

http://www.crucial.com/store/listparts.aspx?model=W3653&Cat=RAM

You can exceed the specced RAM, but there's no guarantee it'll work well. I've done so a few times over the years. Sometimes it's worked without a hitch, other times it's caused the system to be unstable, and other times it's caused it to slow down instead of speeding up.

Though on that crappy machine, I don't understand why you would even want to upgrade the memory. Better to just trash it and get a new PC.

I'm using it for a dedicated minecraft server using Linux crux In a RAM disk configuration.