Your internet shouldn't be lagging using ubuntu, Linux has a really good network stack. Who's your provider? DNS could be slowing you down.
You might need ATI Catalyst Driver version 10.1 or better, that's not recommended for everyone tho.
By the way, Ubuntu 10.04's going to be released in a couple of weeks and Fedora 13's coming out next month. It can take a few days or weeks for the drivers to catch up.