Phew, I'm glad you managed to finally figure it out! Quite frankly, I was running out of ideas. Taking a quick look at your HijackThis log, I don't see anything malicious. One suggestion, though... If you don't want to rename the file, you can open up your mouse options and see if there is an option to disable automatic updating. Or you could try removing this entry in HJT...
O4 - HKLM\..\Run: [IntelliPoint] "C:\Program Files\Microsoft IntelliPoint\ipoint.exe"
As far as I know, the file is non-essential. If this is disabled, then dpupdchk should be disabled as well. To use them, you would have to run the program manually. At least, this is how it should work out. I have never used an IntelliPoint mouse before, so I'm not 100% sure about this. If you want to test it out, I would suggest having a backup mouse just in case you need to undo the changes (you can do this through HJT's menu).
If you'd rather not bother, then simply renaming the file should work.