Craggles_

You may feel inclined to flame, or not dependant on how you respond to newbies constantly picking at you;
either way I'm here for assistance (please help).
I'm not going to tell you what I want -
I'm going to ask your personal opinion, fair ? :) Right,
I'm in the market of upgrading my graphics card,
reason being my games tend to slow down and I'm not thrilled about it.
My current (an intel integrated chipset) can barely handle old oblivion - sorely annoyed.
I've done a bit of research and realised that a) intel integrated chipsets ain't that great and b) they're purpose in life is to sodomise those who wish to buy a custom p.c. who later find out that they're been jipped a lil.
None the less I've always wanted to get a fairly beastly card.
Now - I've looked around and I don't quite fancy an Ati or any of the others (if you see my judgement to be without purpose please do tell, afterall I are newbie) and would like a NVIDIA.
problem being I seem to get varied prices everywhere I go -
for instance ebay,
you'd assume that if you organised a list of NVIDIA's by price you'd get them in order of power nearly.
Whereas infact the price ranges vary so greatly that some sellers are selling poorer versions for a higher price than than some of the higher end versions, leaving me in a jam.
So, I'm in the region of spending 40-60 (more inclined to 60) pounds on a graphics card, (like 100+ dollars or something).
A question: GeForce 8500 GT and the GeForce 8600 GT, is there that much of a difference between them?
Another question: of the 8 series which is generally better to buy for given my circumstances, please.
Furthermore, does memory even really matter.
From my day long research session I've no answer to the first question nor the second and the third I believe a 256mb would show very little improvement when increased to 512mb, is that true?
More research still leads me to believe that if I install a graphics card into my spare PCI Express slot it should automatically swap over
(do i need to uninstall the current graphics drivers first?).
Also - what does a PCI 4x lite slot do?
I've looked around and all I can think myself is that it'd fit a PCI express graphics card - only it won't run it too well, perhaps 4 times slower.
Anyway, if you could help me with any of my queries I'd be most grateful, thank you.

oh p.s. - whats the difference between gts and gt?