File Sharing between Win7 & XP

I'm setting up my home network (W7 & XP PCs). XP sees W7, but can't see folders and W7 can't see XP computer at all.

We share same work group and are both connected to router & Internet.

XP can see W7 but requires a user name and password. Cannot pass authorization (login pane remains)

How do I open the ports W7 says are needed?

Best way to troubleshoot this?

 

Thanks