Balljoints -
You might be having some hardware problems if your system is crashing with a rush of hits. We have customers that do 20GB a day with around 1 million hits on a PIII 500 with 256Mb ram, and have no problems with say a listing on the Hun. So adding ram will probably not help
The other thing that might be the problem is how is your provider capping your traffic ?? Are they using a mod that is built into apache or are they doing it at the router ?? If they are using apache to throttle it down then there is your problem, apache sucks when it comes to capping your traffic, and it will die off if you try to run say 1Gb a days worth of traffic thru a 1/2GB a day cap.
Tim