Ya.......The title says it all.......Norton saved me again.
Every time I start my PC , I have a habit of checking which processes are running and to see if there is any
suspicious process.
From last 2-3 days I have been hunting a process named "msimfo.exe" ........yes it is msimfo.exe.
as some unexpected crashes,slowdowns,error messages were happening.
I immediately came to know that there is something weired going on in my system.
i killed that process.......but it came back after restart(obvious)...and I still couldn't find the source of this....its file.
Then after looking into logs of NIS , I found the info. I needed to really hunt it down.(Source file was in RECYCLER folder)
..Hence I couldn't locate it.
Still amazed how NIS missed it .......I scanned the RECYCLER folder with MBAM.....and it came up with "Worm.Autorun.B"
inside the file msimfo.exe...............I found it. 
It required me a reboot for removal......but after removal...there was no such process running....nor was the file present (Hunting successful)
So even though NIS missed it ......its log catched it......and hence I could remove it.
I can't imagine how much underground/hidden damage could that virus have done if NIS log was not there
Norton saved me again...in a different way !!
Thank you very much Norton....in a different way !!!
NIS 2010 (17.0.0.136) , Xp Sp3.