OT - Why is taskmgr.exe running at 16% - 25% constantly?

[AncientPC]

I ran anti-virus (Housecall), anti-spyware (Ad-Aware), patched OS (WinXP Home SP2). Nothing works.

A friend brought her laptop over for me to fix today. First thing when I turned on and logged in is that CPU usage is maxed out all the time. Turns out Trend Micro is causing most of the damage, the rest caused by taskmgr.exe. Looks the Trend Micro installation is corrupted somehow so I uninstalled it.

Now here's the kicker. When I boot into safe mode, the laptop works completely fine. This leads me to believe that it must be some virus / spyware masquerading as taskmgr.exe to cause the slowdown but nothing was caught.

I'm going to go ahead and start removing things from the registry boot list. Anybody else have any suggestions to try?

I would save an OS re-install as a last resort, mostly because I don't have a copy of WinXP Home and she didn't bring her Dell CD.