ASUS P5E LGA 775 Intel X38 ATX Intel Motherboard

I currently have a PC that I put together a while back using a ASUS P5E LGA 775

The CPU I got at the time was a Core 2 Duo Allendale 2.4 GHz Dual Core

I am upgrading to windows 7 64bit so I can get more memory usage from the PC, and the windows 7 is OEM, so thinking I should go ahead and upgrade the CPU.

However, I am having a hard time finding what CPU's it will support. The listing says:

Quad-core / Core 2 Extreme / Core 2 Duo / Pentium EE / Pentium D / Pentium 4

What does "Quad-core" mean here?

is it this?
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Is the quad really worth moving to, or perhaps I should just go with dual core like:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

or simply moving to W7 64bit (from xp32bit) and going to 6MB of memory should help performance enough.

Just suffering from general bog down of the processor, if more than one account is "logged in", and a user leaves up a browser or two, the other user gets really bad performance. Things just taking a while to come up, like Office apps, graphic programs...

Do some gaming, some graphics, picture editing, internet, programming...

Thanks for any help or input.