Wow.....
I checked the Seagate site and it says it supports Vista as shown here
Answer
When i bought mine from the shop it also came with a different country's Ac Adapter !!!! So i had to use my laptop ac adapter instead which i think may not be providing enough juice since the ac light seems to flash a bit.
However it did start the HD on my vista pc, but no pop up to install the driver ever showed !!
So i tested on my other pc next door using XP all updated. STILL DIDNT WORK !!