Protection for 512 Mb laptop

[amnesia]

I'd go Avira and PC Tools Firewall

[LunarWolf]

Forgot to mention. use comodo or online armor. Both are free and good.

Comodo takes like 100+mb on hard disk but like 5mb on ram
Online armor takes 20-30+mb on hard disk and 20+mb on ram.

[OUSAK]

I recommend CA Antivirus. Affordable and light.

[NinjaRicer]

Hmmm, all around protection? Avira and the last free Kerio version.