New PC wVista Home & Security Software

I
am a novice with a new computer and vista premium.

I want to know, if I never had any other operating sysstem or security
protection software on this computer - is windows defender and firewall along
with my ICP provider security sufficent protection. Should one consider
paying for another full packaged security software and install on their PC?

Currently, a trial version of Mcafee is installed on my computer. I have
downloaded a free version of AVG antivirus. I have also, checked into Panda
products?

Can someone give me some direction?