I think the 2004 version, but not previous versions, of Norton Antivirus (included in Norton Internet Security 2004) has anti-spyware functions. I don't know whether it will remove 123mania.
Have you tried any of the free spyware removers? Such as Spybot Search & Destroy click here
Or CWShredder? click here and scroll down to Official Downloads.
If none of them works, try HijackThis (from the same link above). Unzip the HijackThis download to its own folder, double click hijackthis.exe, Scan. If you're comfortable with removing the rogue items yourself, tick the rogue items, then close all other applications including Explorer windows, and IE windows, and then click Fix Checked. Restart and see how it fares.
If not sure about which items to remove, after doing the HijackThis scan, click "save log", and copy and paste the results here (you'll have to do it in 2 halves), and someone may be able to tell you what to remove. There are also other forums with people familiar with HijackThis logs.