What antivirus for my netbook (Win7) ?

Hey guys,

I have a netbook with the standard specs; 1.66GHz, 1Gb ram ..
I am looking for an anti-virus that is light on the processor and is effecient aswell as being good for keeping me safe online.

Any suggestions; oh forgot to mention i would prefer only free solutions!
Thanks, amcc

I've recently started using http://www.microsoft.com/Security_Essentials/, and have been very impressed with it so far.

I'd use either MSE or avast.