Can I turn off my XP firewall if I have a router? Will I be safe with just the router?
to be honest, you aren't exactly safe with the windows firewall on. a router helps greatly, but for real protection i recommend a 3rd party firewall software. sygate personal firewall is my personal favorite, but it has been discontinued for some time. you can probably still google it and find a download.
It's still safer than no firewall at all.
I mean like will a router suffice and I can just turn off windows firewall. Like if I forward some ports on my router will the firewall cancel this out and I still wont be able to play my games online?
you loose control and reduce your safety-confidence
level. The router will keep ~90% of the junk off your system -- see below
yes it really should, but you should also be able to ALLOW those ports and make this a non-issue.
Any service on your system which has a port-forward from the router will be
subject to attack. In addition, any program which is accessing the internet can
also be attacked -- the firewall is a means to control who get access to what.