What about FreeDOS?
Also, if you think running Linux on a box like that is sluggish, you aren't setting your box up right. Likely, Wine might be a bit too much, but you shouldn't have problems with a version of Linux meant for small footprints or whatnot (try a netbook version, for instance). You could always customize something yourself (go with a smaller window manager - ie, stay away from gnome or KDE); you could even run it without X (command line), though the specs can easily support X. I've been running a Linux with a GUI since the 486 days with only 8-16 mb RAM - it is possible.
Another option might be BSD. Then there are also a ton of experimental OS's out there if you really want to "play around". You haven't really said, though, what your plan for this box is (if it just to run old Windows/DOS software, though, then just drop Windows 98 on it and be done with it).