4 gig Ram in XP?

I used 4Gb in my old PC with XP, but after some hours I Figured out that there was no difference between 2Gb and 4Gb, In my new Vista 64, I felt that the 4Gb really did work, but if your other components lays in the Low-Middle class I recommend you 2Gb, save the other RAM chip to vista

The difference between the system and windows recognizing it is the video caed.
The memory the video card has will be subtracted from the total under windows.
Under normal circumstances XP doesnt need that much memory, but if you game on it you cant go wrong.
Also try to buy better memory than you have
eg 667mhz bus buy 800mhz. The cost will be near the same but if you upgrade you already have better memory.
The faster memory will run at the speed of the slower one but with memory costing next to nothing right now go for the gold.
On any given day tigerdirect is almost giving it away.