1. The PCI-e slots are version 2.0. However, these are backwards compatible (1.1 cards will work fine etc.)
2. For that budget I believe the HD5570 or the GT430 will be the best you can get for your money, depending on your preference. I think they are roughly on par with each other, depending on the game.
What games will you be playing? These cards aren't very strong, and whilst they will handle most games on low/medium settings today they will struggle in the future.