when you say 500k you mean 500kb and not 500MB. Right?
In fact, scanning process, when idle should consume not more than 600-800kb (less than 1 MB).
Open the task manager, leave it there for 2-3 minutes and if nothing is written on you HD or programs running, scanningprocess.exe will go down to 500-800k.
When active, scanningprocess.exe will consume around 13-25MB depending on workload. If you have a single processor you will see one scanning process, if you have dual core you will see two scanningprocess.exe and if you have QUAD you will see 4 scanningprocess.exe. This is normal and by design.
Booting your ZA selectively (as suggested by GURU George) is a good way to see if you have any programs conflicting with ZA AV.