Can someone recommend a good open-source firewall for XP?

sure... (imho) the best free non-bloated firewall for XP is Comodo

http://www.personalfirewall.comodo.com/

Comodo is free but not open-source.

The only open-source firewall I can think of is WIPFW but it may not be easy to use.

This is a new project which may be worth looking at. Many of the other Open Source Projects I have used previously seem to have stopped active development.

Honestly, the best free firewalls are not open-source. I have been using Comodo for quite some time now and am very pleased with it.

True, open source is nice, but sometimes it isn't the best.

Another vote for Comodo, though I only install the Firewall and leave Defense+ out (annoys me far too much and see no use for it).

Comodo is too huge, but it may be ok for my mother.

Here is a good review site for those interested:

http://www.matousec.com/projects/firewall-...nge/results.php

IPTables, seriously.

No port of iptables for win32 that I can find... plus I want something to offer application-based rules and an easy GUI

Thus far, outpost is the only product that offers this but it's not free. Comodo doesn't and is clunky in my experience, and online armor doesn't really do what I want either.