I think David, that that is one of the motherboards that is supported for upto 2gb of RAM? If so then it wont register the rest, although I am not entirely sure. I had a similar problem but was able to download a bios fix, that cracked my motherboard to allow more, but I ended up with more problems, so reverted back :o)
One question? Why on earth do you need or want 3gb of RAM in a home machine? LOL
I just looked it up on the website and it's got a maximum memory of 4 gb so that shouldn't be the problem, I don't know what it could be though as I didn't have any problems going from 1 to 2 gbs.
As for why, I've seriously started to get into computers over the last few months and just really enjoy it. So I guess I'm doing it basically because I can lol.