32bit vs 64bit Win7

Your CPU can read 64-bit instruction, so yes you can use Win7 64-bit.

Win Vista and Win 7, use about the same range of ram.

http://windows.microsoft.com/en-US/windows7/32-bit-and-...

"Can I install a 64bit version Win7?" Yes, but you may need to hunt for some drivers (I ended up buying a new wireless n adapter, no 64-bit driver)
"My Vista OS does identify this a "Win7 ready"? " That means you meet minimum HW spec for win7.
"Is this due the 3GB's of ram?" 3GB is roughly the max you can use with 32-bit windows. (It's less than 4GB because of memory mapped IO, etc.). IF you have more than 3GB of memory 64-bit windows will use it. 32-bit windows will ignore it. (I have a system with vista 32 and 4GB memory. It runs fine and uses about 3.4GB of real memory.