I'll leave the analysis of this to folks on the CIFS team, but, as an FYI for those who might be curious:
Windows 4 Samba
Session Request (No mention of this packet in Leach) Flags 0x81000044 0x81000048 Source "WU" "RECYCLE"
Session Granted (No mention of this packet in Leach)
Those two packets are probably NetBIOS Session Service packets; see RFC 1001 and RFC 1002 for the spec on how they work in NetBIOS-over-TCP. The CIFS Internet Draft might refer to those RFCs.