Not a bad spec as you say, but something is bluting up the works somewhere. I know that I have said this on many threads and I am no Microshaft apologist either, but the free MS anti Spyware proggie does much more than it suggests. There is a very good facility for seeing exactly what processes are running and to which program they belong. Something is clogging up your machine as a start up file or program and this would be an effective and easy way of finding out exactly what. I take it that you are already doing this?
One thing I DID notice with your spec. was the online scanning thingybob. If it does what I think it suggests, then it is surely duplicating what Norton AV does and I wouldn't have thought it was going to help one iota. If it were me, that would be item one to disable, in order to narrow down the culprit.
Another thing, but I have never used an iPod and can't see the chance of it happening really - but it does with my PDA (Windoze Mob 5) Norton does cough a bit and try to scan the attached device as well. Does your machine boot cleanly when no ipods are hooked up? My number two attack would be in removing the synch software ( I don't know of any ramifications here with Digital Rights Management for instance - so a quick RTFM might be in order, just to be safe) and then checking performance. (My own MS sync software is a bitch and has caused more aggro than I can believe)
After that, even if the above has not worked, it will have narrowed it down somewhat. Let us know how you go on.
Good Luck!
Conan