Hi R. Richards,

In fact it is true that two resident scanners will conflict. It is like two dogs guarding a house start to fight each other and let the intruder pass. The same could be in combination with a non-resident scanner if the signatures will cause a second resident scanner to react, so do not combine avast with non-resident panda for instance. Resident and non-residents like online scanners or downloaded scanners like DrWebCureIt or tools with the latest signature-scans like Stinger.exe can be used next to each other.
I myself combine non-resident avast with ClamWinFree Antivirus and DrWebCureIt (keep these updated constantly), I also use COMODO BOClean 4.25 & Trend Micro RUBotted. In-browser scanning is done with DrWeb’s hyperlink av-scanner plug-in for Firefox and IE7. Crap is cleansed with ClearPrivateData in my portable browser, together with ATFCleaner and ClearProg before closing a computer session.
I minimize the risks of infection further not using full admin rights on the account I surf with and using SafeXP. Occasionally I run HijackThis to clean out the occasional non-necessaries.

polonus