I've been using a freeware program called RRTrains 2000 successfully under Windows 7 (the program will work all the way back to Windows 9X).
For a long time I had only put in a few lines worth of test data, but after finding some of my old paper records (the most recent ones are still missing) I've been steadily adding data to it. Now up to about 270+ records.
It doesn't have canned manufacturer listings, but that's okay in my case since I have stuff that probably isn't listed in anyone's pre-defined database. It also supports user-supplied photographs and has allowances for such esoteric minutae as coupler, wheel and truck types, dimensions/weight and even loads.
As you might've guessed, it's not O-gauge specific, but I've been able to make it work. It's a small download (464k), and there are other features listed on the developer's page linked above.
---PCJ
