I need to mark this Post as SOLVED...but not sure how to.
I was reading some other Posts on Spyware...and came across a suggestion on running AVG Anti-Spyware(Full - trial version). I installed it and ran it...and it detected: TROJAN.AGENT.ABN and a Medium level Cookie that had a name similar to the pop-ups i was getting. The Trojan was successfully Quarantined and the cookie deleted. I no longer get that WindowsSecurityUpdate.exe window at startup and no more pop-ups.
But what puzzles me is...how come my TrendMicro PC-cillin Internet Security 2006(virus & spyware scans)...my fully Paid version of Spy Sweeper (scans)...Ad-Aware SE Personal (scans)...or Spybot S&D (scans) detected NOTHING!!
Frustrating!!!
Anyway...thanks for the replies!!!