UDP/137, UDP/138, TCP/139.
Having said that, DON'T DO IT
Problems from your side:
Very very very insecure. Your asking the big bad wolf to come blow your house down.
Doesn't work well across subnets. Will be a real pain to get it to fly.
Problems from my side:
You will send a lot of broadcasts to the public internet. If you happen to be my neighbor, ie, we're sharing the same cable segment, I might come blow your house down. Well, don't guess I would really do that, but I probably would complain.
Of course, if your firewall your trying to tear down is between two private networks, I don't care about the broadcasts.
If you really need access to shared resouces, consider using a VPN. Deals with the security and broadcast issues quite well. Browsing across subnets can still be a pain, but it is easier to make it work with the VPN than without. No additional cost, modern versions of Windows have a built in VPN server and client.