Reinstall of viruses

I have a rather strange problem, my sons PC keeps installing several viruses (trojans) every time he starts internet explorer in win98. I keep removing the viruses, but cannot find the installer as it is not a virus but just a link of some kind. I have tried several different programs to remove it, still no luck. Some of the names that show up are: ntwg.exe, netpg.exe, cryg.exe, msrp.exe, etc.... It keeps changing, though the virus scanner says its a trojan downloader (trojan horse downloader.agent.5.L is one example). Cwshredder restores 7 pages in IE each time the program is run. I could you some help.

Hi gyronutjoe,

Please download HijackThis. Make sure you install HijackThis to a permanent folder such as C:\HJT as it creates backups of what we will fix. Run the program, press Scan, after a brief pause... press Save log. Notepad will open, copy and paste the entire log into your post. Do not fix anything yet, most of what's in the log is needed!

http://www.majorgeeks.com/download3155.html

Tom