Oh my... :)
Well, the installers will only run on XP and above (well, in practice it's Win2000 and above), so you would have to install the game on a compatible system and copy the game's installation folder (apart from the image file/files, described below, if there are any present) onto the old 486, somehow... ;)
If there is a large file with the .gog extension, accompanied by a matching .inst file, rename them to .bin and .cue, respectfully. Make sure to always edit the .cue file afterward, so that it will point to a .bin file, rather than a .gog file. You would then have to burn the image's contents onto a CD.
If the game's soundtrack is in .ogg format, rather than Audio CD, you would have to burn them onto a CD as an Audio CD - make sure to leave the first track empty, as that's where the game data would normally be. :)
After all this this done (you've copied the files and prepared the data/audio CD/CDs), you would have to launch the game from your command prompt (or Norton Commander, or whatever;)) like in the old days. Look for an appropriate executable - naturally, DOSBox won't work on DOS. ;)
I'm afraid I'll have to leave the hassle with tweaking your autoexec.bat and config.sys (if needed) to your imagination, though. :D
Be sure to thank Grah for explaining the bit about image files in a way I could understand. ;)