I'd try CGminer instead.
I've tried CGMiner (both as the option in 50Miner and as the standalone) and neither work.
I just noticed the console printed out.
btcguild.com:8332 04/03/2013 17:50:58, Verification failed, check hardware!
During the time it's been running it hasnt generated any shares.
Verification failed, check hardware is a message coming from your miner, not the pool. It means you're having severe problems with the hardware and it is not reporting valid shares. Have you tried updating your drivers?
The catalyst control center says it is on Catalyst Version 3.2.
Essentially I went here:
http://support.amd.com/us/gpudownload/windows/Pages/radeonaiw_vista64.aspx
and downloaded the latest driver. Im not sure why, just seems to me that the driver names are odd; sometimes I cant decide if it's a version of the control center of of a driver.
Edit: Not sure if you will see this edit, but... The miner ran for approx 6 minutes from connecting to BTC Guild until it gave the hardware error. During that time it (again) gained no shares.