Suggestion on firewall


I have

1) netgear n150 wifi router. I also has a unused nokia siemens adsl modem. Here the net connection is pretty much like connecting to lan. 

2) Dell latitude 3440

3) assembled CPU 1gb ram 2giga htz dual core processor 


Now, I want to set up a firewall.

Can I use my assembled cpu which I'm no longer using as a hardware firewall? if so please suggest how. 


I think netgear already has some features which gives good security. So would this be sufficient? 


I don't have any crucial data but I just want to learn. Please help. - so i dont understand your 3rd option there.

If that is a full computer then get at least 2 1GB (preferably intel) NICs. then put on there and that will i think give you everything you need.