Question on the litest Windows Anti-virus

[coius]

I need to know which is lighter on this system:

Pentium 233Mhz MMX

128MB PC-66Mhz

40GB HDD

DVD/CD-RW (pulled from another machine)

These are the two anti-virus I am looking at:

Avast!

or

AVGFree

I need to know which has the litest memory footprint and which requires less CPU Cycles to do active-protection

I need these to be in free mode though.

 

[Cory5412]

I'd take AVG purely because it's what I use on all of my other systems, but for pure lightness, if you can get ahold of Sophos AV, (which isn't free unfortunately), that'd be awesome. Sophos is lightweight purely because it doesn't do any actual work.