you need to open up ports for netbios traffic e.g.
tcp 139, 137, 135
see this link
http://www.cisco.com/warp/public/110/pixfaq.shtml
Q. I need to allow my users access to shared folders on my NT Domain from remote locations. How do I do this?
A. Microsoft's NetBios protocol allows file and printer sharing. Enabling NetBios across the Internet does not meet the security requirements of most networks. Further, NetBios is difficult to configure using NAT. While Microsoft makes this more secure using encrypted technologies, which work seamlessly with the PIX, it is possible to open the necessary ports.
In brief, you will need to set static translations for ALL hosts requiring access and conduits (or access lists in PIX Software 5.0.x and later) for TCP ports 135 and 139 and UDP ports 137 and 138. You must either use a WINS server to resolve the translated addresses to NetBios names or local properly configured LMHOSTS file on all your remote client machines. If using WINS, each and every host must have a static WINS entry for BOTH the local and translated addresses of the hosts being accessed. Using LMHOSTS should have both as well, unless your remote users are never connected to your inside network (for example, laptop computers). Your WINS server must be accessible to the Internet with the static and conduit commands and your remote hosts must be configured to point at this WINS server. Finally, Dynamic Host Configuration Protocol (DHCP) leases must be set to never expire, or better yet, statically configure the IP addresses on the hosts needing to be accessed from the Internet.
A safer and more secure way to do this is to configure either Point-to-Point Tunneling Protocol (PPTP) or IPSec encryption. Consult with your network security and design specialists for further details on the security ramifications.
