Gents, Ladies, Confused intermediates;

I wish to upgrade my puny febrile graphics capacity. I currently use an NVidia Geforce 7500 SE, which I suspect is an El Cheapo type card.

Anyway I think I have two problems to overcome before I can proceed:
1) I don't know how much juice my current power supply generates, or the rest of the PC uses. As a result I'm unsure as to whether I need to buy and try and install a new one (oh joy....). Is there any utlity on the net I can use to judge this? Or is it just a matter of looking in the case (I'd prefer to avoid opening it more than needed as its a pain to get back on).

2) Anyone have any thoughts on what would make a good not too bulky (I.e. not a two slotter monster) and relatively decently priced NVidia graphics card to replace the current one?

I haven't got a clue about current graphics cards... the name numbers and the power don't seem to relate logically anymore.