Soriku, hijackthis is useful but it won't do the job by itself. Download these programs and run them in safe mode, they removed about 95% of malware and trojans:
http://www.bleepingcomputer.com/files/smitRem.php
http://www.bleepingcomputer.com/files/smitfraudfix.php
Then post hijackthis log so we can get anything else removed.