I can upgrade my ram up to 4gb max. I'm running Vista 32bit, and because of this I can only use 3gb of ram (that's what I heard). If I install 3gb can I do 1x3gb and occupy 3/4 slots? Is it ok to have one slot empty and not "pair" it?
Also, I have a graphics card that's 1gb. Does this mean I will only have 2gb ram (3gb-1gb gpu=2gb available)? Does gpu ram affect pc ram?
From what you've posted, as I understand it, each slot can take 1GB max. so if you want to install 3GB you will need 3 x 1GB RAM modules, installing each module in three of the four slots.
That will leave one slot empty, nothing wrong with that.
Your graphics card, if it's an add-on card and not integrated on the motherboard, has 1GB dedicated video RAM and therefore does not use any system RAM like an integrated (on-board) video adapter does.