This is sort of a long shot but...
We recently built a new Windows 2003 R2 Standard server on an IBM server. Dual-Core Xeon 2.66 with 2 GB RAM, 2 x 1.0 Gbps Broadcom NICs teamed for NLB/Fault Tolerance, 2 x RAID 1 - 160 GB Hard Drives.
3 Drives - C:\ - System\OS, D:\ Data, E:\ - External SATA Storage Array (2.8 TB)
There are spread shares on both D:\ and E:\ that users (Windows XP Client workstations) access, about 50 users. The problems is the connectivity is intermittent and it occassionally drops so that when users are saving it takes forever and/or it sometimes "locks" the whole server so UNC browsing and file access is cut off for everyone. Only way to fix has been to reboot.
Contacted Microsoft and they could not find anything wrong. This is, obviously, a big problem as it is a file server. The server is completely updated with all MS patches. An iPerf test from the client workstations to the file server gives an average of 200 MBytes for Transfera nd 180 Mbits/sec.
Event log only shows Errors for the Symantec Tamper Alert (Anti-Virus) due to having the User Hive Profile installed (EID 45).