Setup new network...not sure if vulnerable

[QuietFlight]

All comptuers are on Windows XP

Heres how i got mine up:

Went into Network Places->installed NWline Net bios->went to internet protocol(tcp/ip)->advanced->WINS tab-> Under netbios setting clicked "Enable netbios over tcp/ip...the ok'd out of everything.

I did that to 3 computers, all are seen over the network and all are sharing files

Is this the proper way to set up a network of computers to share files?
Am i vulnerable to people getting into my computer?
I'm not sure how to effectivly use the "Permissions" button settings, can anyone give me some insight?

 

[QuietFlight]

oh yeah all are connect to a router....all are on behind firewalls