... or you could buy the game on Zoom Platform for a fiver. It's the only store still selling digital downloads of the old Duke Nukem games. From what I've heard, "they have a perpetual license to sell the Duke games that Gearbox cannot revoke". I have never used Zoom Platform myself, so don't bother asking me anything about it.
By the way, I just installed the full version of DN:MP that I got from the cover disc of a gaming mag on my Windows 10 machine and it worked fine (using DirectX, 1024*768, windowed). This version, coming from a cover disc, obviously doesn't have copy protection. I haven't tried my other copy of the game (retail release, probably using some sort of copy protection, but not necessarily the same one as your copy). That means the game itself should at least start under Windows 10 (64 bit) once you get past the copy protection.