about: Blank???

[Dudelive]

Help is needed here on this. At work on the computer there has occured a file named "win32.trojan Downloader.agent.al" which has been detected by Trojan Remover V6.3.5 with updates. Also Ad-Aware SE keeps on detecting all sorts of malware....COOLSEARCH as well as many others. After throughly scanning with Symantec, Ad-aware SE, and Trojan Scanner 6.3.5 and all is cleaned. When you open IE 6.0 w/ updates, it will keep displaying "about: Blank" as the webpage instead of Google when you open IE. What are the best ways to solve the problem?

I can NOT do a clean reinstall as some of the software can NOT be reinstalled except by the company that owns the software and they really charge for their services to come out when they get ready.

Please give advice as to a real good correction.

WindowsXP
Symantec 9.0
ZoneAlarm 4.0.123
Trojan Remover 6.3.5

Thanks
Dudelive