In Registry: HKU/Software/Microsoft/S-1-5-21-(blabla)/Search assistant/ACMRu/5603, I see entries like 000 *.ject, 008 Gigex speed delivery, 024 gator. Norton, Ad-Aware, and RegSeeker show no identifiable problems, and HiJack This shows nothing out of the ordinary. I there anything to be concerned about? I run with Norton & Zonealarm, and use PestPatrol about weekly.

Simple solution !
Go to the registry, do a search for ACMru and delete the folder and all
it's subfolders.
Normally you will find a backdoor trojan agent like "A0030882.exe" and
similar. No matter how often you run your virus scan that has picked it
up, and yet unable to find it to remove, so I resort to the registry to
delete these stupid files.

5603 just happens to be a subfolder of ACMru.
Just delete the lot. I do without hesitation and have no problems. Just
reboot.