Chances are if you've got one trojan then you've got a few. You will need to use a few utils to clean it.

We use Microsoft Security Essentials, free download from Microsoft, Malwarebytes as already recommended plus SuperAntiSpyware and sometimes Adaware, all downloadable from www.download.com.

Download and update each util, then remove network cable or switch off wireless to ensure the trojan cant re-infect itself from the 'net. Start one of the utils off, leave it for ten mins, then start another off, might take some time depending on spec of pc. Also ensure to run full & complete scans rather than quick scans.

Depending how pc savvy you are run up msconfig and check the startup items for unusual .exe's. Google them if neccessary from another PC to see if they are malicious and unselect from startup if the are. (Start button, click "run", type msconfig into the run box.)