I have similar problem on XP-SP3 and also have AVG free on the system but when I uninstaled it, 108.000K remains!!!
I also have notification in Security Center that AVG antivirus is turned off, WTF!!!
I try everithing to solve this problem but nothing worked : cleaning whole PC with Reg Seeker,CCleaner,Glary Utilities,Disc Cleanup,Reg Cleanup,Defrag,repair system files,explore services and proceses...
Try also scann with Hitman pro,MBAM,SIS,Avira,Panda,MSE...but nothing helped and I decided to reinstall OS
Now I have win.7 and Sistem memory usage of 56K
MY RECOMENDATION : Don't use AVG product of any form!!!