3Mhash/s is very wrong, 300 is right...
download Bitcoin, RPCMiner and set up an account at mining.bitcoin.cz. Everything went pretty well, made an account and managed to set up RPCMiner straight away and start mining.
Uhm, let me guess, you downloaded a CPU miner instead of a GPU miner?
What about using GUIMiner of CGMiner?https://bitcointalk.org/index.php?topic=3878.0
(CGMiner is good but no gui
Also if you mine on a pool you don't need to run the Bitcoin client. Sure, it's not a bad idea, having it run is having one more node in the network having the whole blockchain and relaying blocks and transactions, but isn't required for pool mining.
It's for P2Pool, if you are interested in trying it.