A huge old Windows 2003 machine is sucking power like a highly paid prostitute. And you aren't using exchange? Why did you even consider Windows 2003 when you could have built/bought a Linux/Unix based server for quite a bit less. I mean, the license per seat of a Windows server is probably upwards of $1K for about 10 people. Isn't it? I know Dell and others were selling non-Windows servers over 10 years ago.......
I'd wholeheartedly recommend getting a NAS. I have a Synology DS1512 that I got in April, upgrading from a ReadyNAS NV that I had for 5 years. Nothing against ReadyNAS/Netgear, that unit was robust and I never lost a single byte of data even though a few hard drives failed on it (gotta love RAID5). It is now serving as a backup device for my Synology unit.
Anyhow, the Synology unit is LIGHTYEARS ahead of the Netgear stuff in terms of software and hardware. They have a whole line of stuff from 2 disk units to like 16 disk units. All of them run the same software. They are easy to configure, and maintain. You can easily set it up to be able to share files over a VPN with it. Or your can log in via the web and get documents. Or have it stream music and videos over the internet for you. Macs, PCs, whatever can hook up to it. They even have iOS/Android apps to monitor or access files from it (like a streaming audio app, video app, etc).
The software and hardware is sound. I had a flakey DS1512 initially, buying it like the day after it was available. Some sort of ROM patch was needed. Synology was fairly good about providing me with a replacement (I did have to complain a lot to their support people). And the current 4.1 beta of their software is causing random crashes on my unit......but it is BETA after all. The release version is rock solid (DSM4). My DS1512 was running that since I got it and it never had any issues at all.
I'd say that hands down, when I was researching a replacement to my aged ReadyNAS NV, the Synology software and hardware was the winner. And it has proven so far to be true. And I still have two more drive bays to fill on it......;-)