that if you hook that harddrive up as a slave on the same cable as the W2K harddrive that the programs running and installed already on the W95 HDD will still work because it has it's own Windows directory still intact so the program will be able to still find any system files it needs to run just fine...without a dual boot. All you should have to do is right drag a CAD program shortcut from the D drive (which will be the W95 drive) in windows Explorer of W2K from the W95 Windows\Start Menu\Programs list that will still be there...and when you get it to the desktop, let go of the mouse and choose COPY HERE.
Then click it to see if it works (it should).
W2K is NTFS whereas W95 is FAT16 or FAT32 and as such if you use the W95 as the Master instead of W2K on the cable, W95 will never see the W2K harddrive, but W2K should have no problem seeing the W95 drive and all of its folders and files in Windows Explorer.
There is also a suspicion on my part that the CAD program is a DOS program and may not have written any of its files to the W95 system folders and would have all of its needed/required files to run located inside its own folder structure under the W95 Program Files\CAD (or whatever the company name is) or just a separate folder under the D drive. If that's the case, you might try using the installation disks that he has for CAD and see if it can be installed at the W2K desktop and actually work.
If it does, then let it install to the default location that it wants to install to, open up some of those folders in the W2K Windows Explorer and see where the database files are located (they will be empty on the W2K machine). Once you can locate the database files on that drive, you can right drag the ones he has on the W95 drive from that same location to the W2K location, let it go, and choose COPY HERE (never, never, never, choose MOVE in case it doesn't work). You will get a window that asks if you want to overwrite the existing file....say yes, since the existing one that just got installed is empty and you want to replace it with a working database.
Once you have COPIED the database files he wants to keep.....then you an use the W2K CAD install icon from the Start\Programs list to start up the program and see if his database is working. If it is, and he has everything working properly on the W2K side of things, you can physically remove the W95 harddrive from the slave position on the cable, and know that you have pulled off a wonderful copy trick.
If the CAD program won't install on the W2K system at all, it should still work on the W95 drive....and if it does, and if the system has a burner program and a DVD burner installed on the W2K, burn the whole W95 harddrive to a dvd cd as DATA....this should work if the W95 harddrive is less than 4GB in size that's used up space. Otherwise, burn the whole CAD folder instead and hang on the installation disks for the CAD program. This will salvage his database files in a safe place in case that old W95 harddrive dies off one day. Replace the drive, install W95 on it again, install CAD again, and then copy the CAD folder or just the database file that's on the cd back to the new harddrive to the same location and overwrite the empty one again.
This all sounds confusing as all get out, but once you get the drive hooked up as a slave, and open up the D drive, you have options now. Just remember you want to right mouse drag and COPY HERE.......never MOVE. That will always give you a way to safely find out if things work and not lose the data in the process. If necessary, get paper and pencil and make an outline of steps you want to try for the options you might have. Go with the one that works and X out the ones that don't, and logic will steer you since most of what you will be doing is in the Windows Explorer window which is already familiar ground.
I've played around with this kind of stuff many times over the years, and most times, have been successful...just take your time, and you should be fine.
TONI