so i go the the nvidia site, and theres drivers, all updated. but there are drivers for 4-9 series and then a 200 series, the 4-9 all accept my card (7100) but whats the difference, a lower series does give me a lower frame rate but what are they for?
No. When you go to download the driver you're asked what series card you have.
The older cards have probably been optimized as much as they can be, the newer cards use different, newer technology, architecture, etc, etc and are just starting out thier optimization, tweaks, fix and whatever else cycle.
The newer cards can do more things, DX10 for example, which the older cards simply cannot, so why update them with stuff they cannot use.