I want to add more memory to my system, currently running 2 GB of Corsair DDR2-800 RAM in dual channel, i know i can't do 4 GB due to 32-bit limitations, but can i do 3 GB and will Windows recognize it? If it is possible is it better to get 2 512 MB sticks and run them in dual channel or just get one 1 GB stick in addirtion to my existing RAM?

Yeah you can use it. Only thing is it'll probably show up as 2.99GB or something. Nothing to worry about though, it'll work fine. For best performance, if you have dual-channel, color-coded slots, put two 512MB sticks in one pair of slots and put two 1GB sticks in the other pair.

Cool, thanx Rage! My mobo does have 4 color coded slots, 2 of one color, 2 of the other, i guess that means i can do this, i think it supports up 8 GB. Anyway, are there any special changes i need to make to Windows/system to run 3 GB? Or i can just put them in there and fire it up?

Caution

I would not attempt this without a motherboard manual outlineing
it's memory type and slot sizes.No paper manual,download a pdf.
You can't just stick any brand,type or size memory into a slot,
because it fits.

He most likely knows they're DDR2 slots. And the only motherboards I know that are picky about memory are ASUS ones. Others accept any sticks just fine. And good-quality memory is not very expensive nowadays. Even el cheapo RAM does the job pretty well most of the time.

You can have 4 gb of Ram even on a 32 bit system.
The issue is more about it wont take advantage of the full 4 gb but it will still be more than if you 'just' have 3 gb of ram

Also, though I am not 100% sure but if you are running 2gb in in dual channel now, adding just one stick more might disrupt the dual channel thingy and slow down the system. At least that was my thought when I went from 2 gb to 4 gb, I did that so I could run all the sticks in dual channel mode

Anyone got any comments on that?

yes you can, but unless your board can handle MULTI-channel ram, your systems ram will be asymetric and will slow down.
XP can address up to 4gb of RAM. It is always best to add ram in even pairs unless you have a multichannel board (more than dual channel).
There are only a few multi-channal boards. The MSI K7N2 Delta 2 is an example of a multi channel board. I have 1.5 gigs of ram in mine.

@Tedster, does a multi-channel motherboard have differently color-coded pairs of slots? 'Coz that's what I think he has. But yes, the RAM absolutely has to be of the same speed to work correctly.
@flowerpower, I think you can just put the RAM in and fire the PC up and it'll work.

generally yes. Multichannel boards usually will have different colored slots.
RFTM the motherboard manual.

Guys, not sure if my board is multichannel or not, i have a Gigabyte GA-M59SLI-S5. I know what memory to get for this, i currently have 2 GB of Corsair TWIN2X2048-6400C4 so i'll get 2x512 MB of the same RAM, so that's not really a problem. My only concern is that the mobo manual says that in order to run 2 pairs in dual channel it is recomended that they be of identical brand, size, chips, speed. The brand and speed is the same, but size and chips is not the same, i think the only way i can do that is buy a 4 GB 4 stick kit. It is only a recomendation on Gigabyte's part so may be it will work, if not i'll try run 4 GB.