Eriisa: SpyBot actually has a warning when you first start it giving some sort of warning about the Ad-aware program - but I never had any problem.
Also - I DO NOT use any type of feature of any of those program to let them run in the background while I'm doing other things - I simply use them as stand alone scanners. I have not tried the Spyware Terminator yet - but did notice when I went to download, you have to be carefull to get just the Spyware Terminator - and not the one that includes some sort of "web security" which I think runs in the background all the time.
I just use these occasionally to scan my PC.
So if you are running 1 in the background and try to use another one at the same time - then yes, there might be conflicts between the programs.