In my years of working at home with W2003 server, Enterprise mostly, i found out that the hard part is to find answers, problems are there where you don't expect them. In this case i had msmpeng.exe shooting in the 100% during transfer files to the server and now it is interrupts when i want to read from the server. This hardware is an old Compaq EN series pc with P4 1.00ghz with 4 GB memory. As a SATA harddisk solution i use a pci, 3 ports raid-3 XFX-card. In this machine, and with this same config, i had a single disk as the C-disk, until there was a bad spot on this 10 year old datacarrier. I had to reformat it, (IDE) and bought a second HD and mirrored it for sure. I started to install W2003 server on it, i downloaded SP1, SP2 and installed it on the server, Then i updated everything, and in the end i gained acces to the RAID-3 disk, i made sure the server admin had all the rights. Well, since this problem i read here on this board, i had it before, but it is so unpredictable wether it is the disk where the system resides, or the data (raid), or is it the old hardware, or the network?
In this way i can't really tell. Until i have the money to buy a good datastorage for my medialibrary, i'll keep trying to find the cause. I have a similar pc, and i think i'm going to testrun this pc and elevate it to server, see if the problem reoccurs.
I'm sorry that i can't give you a straight answer, even Microsoft can't give it, there are so much factors. I say, try to reinstall a fresh server on a replacement harddisk in the same configuration, maybe that'll help.
Ps. currently copying a 6,5 GB file from server to pc, well, a 11Mbit wireless connection is faster!