I don't know how well The Dig runs on either 95 or XP natively (if at all). However, there is an excellent DOS emulator floating around in on the interweb called DOSBox (http://dosbox.sourceforge.net/
). Just follow their instructions for mounting your CDROM drive (or hard disk, if you so choose) and set your sound card options to the default SBlaster16 settings from within The Dig launcher itself, and you should be good to go.
Of course, you can try
running it under XP, but I doubt it'll work. You might have better luck with 95. I suppose I should test that myself, but I really have no need to. :P