Hi,

Realistically CPU and GPU mining aren't anywhere near worthwhile now.

At 300 Mh/s you may make 20 cents a day which won't come close to paying for the 150w+ needed to run your GPU.  You can get an Asicminer USB block erupter for under $20 which has the same hashrate as a fast GPU but only takes 2.5W of power, but even with this you are unlikely to break even IMHO.

Have a look on ebay for "ASIC Bitcoin" or "Bitcoin miner" to see some options.

Cheers,
o999.