I'm a NAS/SAN Engineer at work I've got a $300,000 NAS system at work that is ALMOST as reliable as my Linux Samba server running on a $299 Dell in my basement. OK, so the one at work has 10,000 users and 10 TB behind it vs. 4 users and 80GB. On the other hand, the work one just runs a tweaked version of Samba.
The point is, take a look at Samba. You can configure it to be a Windows domain controller, and set up shared file areas. It's a great place to store arcade cabinet hard drive images! You could even store all your cabinet's ROMs there for one easy place to do updates. Get seriously carried away and take the hard drives out of the cabinets. Figure out how to boot from the network and access everything over the network.
On a not-so-related note, has anyone considered anything like VMWare for multiple arcade cabinets? The concept is that it allows multiple "virtual machines" on one computer. If it can output to multiple monitors and take input from multiple "keyboards," maybe it can control several classic MAME cabinets from the same computer. One problem I see is that it uses a "virtual" VGA adapter - meaning no ArcadeVGA or otherwise tweaked video adapter.