exe downloads, and for me at least the in game lobby still actually works great for lan matches! No drm, no registry tweaking, no cracked. However, for simplicity, you could consider the Gog 'warchest' version? Im not sure that Allied Assault is available on Steam at the moment either.
In that instance, your best bet probably would be using those kind of tweaks and edited. If you are running a retail disc for whatever reason, then its going to have the drm. The retail discs for Allied Assault have safedisc drm which can cause problems with Windows 10 unless you look into specific work arounds - as some people here have wisely mentioned.
