I have been programming in FoxPro since ver 2.0 and have had to make adjustments all along the way. Versions 2.5, 2.6, 2.6(W), 3.0, 5.0a and soon 8.0.
Each version had its own problems.
My first consideration would be, 'What if I have to re-install FoxPro after upgrading to Windows 2000?'
Fox 2.6(D) will not install under Windows 2000. The work around for that is to record the folder where the FoxPro program is installed to CD. Copy this folder to another hard drive and it will work fine, and so will your applications. Remember, this is a DOS prog, fully self-contained. I know this since some of my legacy progs are still running under v2.6(D) on Windows 2k machines and I have had to adapt.
It's scary to take the plunge in to an upgrade, especially one as far as you are facing, but there is plenty of help out here, this site being my favorite.
Micorsoft has published new support criteria for its progs. The norm is five years from release date. In the case of Fox 2.5, this is long past.
When was the last time you saw a forum on dBase III+?
With the quantum leap you are facing, you will probably have to rewrite most of your app's. However, with the RAD development tools in Visual FoxPro, it isn't as bad as it sounds.
Projects are still projects, but screens are now forms.
Reports are still reports and labels are still labels(but far easier to create).
The wizards in VFP will knock your socks off! compared to FoxPro(D).
Your .exe's will be smaller. If you have numerous app's out there on the same machine, you only need to do a full install once. The windows files only need to be there once.
Then you can install the numerous .exe's by just copying them in the folder they need to be in. My .exe's range from 350k to over 2.5M. These are still relatively 'small' app's.
You also have the advantage of 32-bit with VFP. And yes, the same app running on a 32-bit system will run faster than the DOS app running 8 or 16-bit.
My suggestion is to upgrade to ver 7.0 or download the free eta that is available from microsoft. You will need Windows XP or Windows 2000 to run it and make sure you back up properly before installing.
I know I sound like an advertisement for Microsoft, but there is a whole new world out there, untapped. And NO, I don't work for Microsoft!
Use your own judgment, and good luck!
Pat