I have changed to vista a couple of weeks ago and are now goin back to xp. yes i am upgrading back to xp.

But since i changed to vista i changed my DDR2 mem from 1.5gb to 4gb.

It is well known that xp is restricted to just 4gb but does this restriciotn include your video mem.

I don't think so.

I thought XP only recognized 3gb of RAM?

I believe there are 64bit versions of xp that allow above 4gbs. YOu also have to get a 64 bit version of vista to have more than 3. something GBs of ram.

i think xp64 recognizes more then 4 gb i could be wrong though, video memory and system memory are separate so you can have 4gb ram and say 512mb-1gb video card

Depends of your hardware, but usually it keeps around 3.2 Gb...

XP only recognizes up to 3GB of RAM.

32 bit operating systems can only address 4 GB of RAM, and various other components (like your graphics card) nab some of that address space so your OS will only show 3.X GB. If you have a 64 bit OS you might still run into problems if your CPU or chipset are uncooperative, but usually you're in the clear.

at the mo i am using vista 64 and it recognizes all 4gb

You need to change your boot.ini to accept the 4GB. I had to do this for a couple of computers at work.

Google it and you should find something.