I'd try the latest drivers. If those don't work too well, try the latest omega hacked drivers. If those don't work well, toss the card into your circular filing cabinet (trash can) and get another card.
Seriously, I've never heard anyone who was truly pleased with an nvidia 5xxx series card. Even the GF4-4200 is faster than most nvidia 5xxx cards except for when running directx-9 specific stuff. If it was free, then use it because they're not exactly "bad" cards, but I know a few people who felt their 5xxx cards were a step backwards from their GF4-4200 or 4600.