Dave, in addition to potential use as a fileserver, the ML330 would also be a good machine for post processing and OCR work if you ever decided to start scanning your large collection of vintage electronics magazines and books. For that fact, with two machines, assuming your internet connection in the lab would allow for it, you could use one machine for post processing and internal file storage and use the other as a publicly accessible archive. Another potential use for a smaller machine would be gps locked ntp or you could run your own internal network services such as dns, dhcp, etc. I've found an embedded machine with a Pentium M can work very well for network services on a small network though, so even the smaller of the two machines would really be overkill for that task.
HP will generally also supply restore DVDs for these machines if you contact them. The original OS might not be something you'd want to run, but the utilities and configuration software would still be worth having. Of course if you decide to sell the machines, the restore discs also add a good bit of value too.
The thing that puzzles me about the ML330 is that it has 3ea 8GB and 3ea 4GB memory modules. Usually these should be installed in matched sets so the system can use a faster interleaved memory scheme. If the modules lack an extra HP sticker on them, I suspect they might have been customer upgraded/replaced and they didn't know that they really should be installed in matched sets. Of course another explanation is that someone else beat Dave to the machines and nicked the hard drives and a couple of memory modules...