Generally, it's no problem for the Mac to grab files that the PC is sharing, there's a perfectly reasonable SMB client implementation in OSX and from memory I don't recall it having any problems doing NetBIOS name lookups, so it should be no great drama.

Just hit Apple-K in the Finder (or the same thing via the "Go" menu in the Finder) and enter the "smb://" prefix followed by the name of the PC you want to connect to in order to let it know that you want to use SMB file sharing instead of the default (which is afp:// which is the AppleTalk File Protocol, i.e. the Mac native sharing). It should then give you a login screen where you can enter in some credentials known to the fileserver and then you'll be able to pick the particular Windows share for the Finder to open.

Going the other way is much, much more difficult, though, even with the server edition of OSX. I wouldn't recommend that you attempt it, just stick to using the Mac as a client and the PC as the server.

In the interest of any others who may read this thread, I've had good luck using Linux as both a SMB server and SMB client.  I can share files both ways between Linux and Windows.  I have no experience with sharing files between Linux and Mac, but, as is the case with Windows, it should work well if Linux is the server and MAC is the client.

In a Linux/Mac/Unix environment, NFS is another protocol useful for sharing files.  I've found it to be more stable than SMB, but not as flexible.  It provides good control over what users are able to access what files and allows them to be accessed seamlessly, but all the files need to be on a central server.  There are also some difficulties using NFS through firewalls and security tunnels.  Finally, I've never found a good NFS client for Windows, so that option is out for Windows users (unless anyone can suggest a good client.)