I agree with everything barythrin says. I'd just like to add that FreeBSD has another real plus. It has a manual which works. You can buy the book or use it on-line. I'm sure it's not perfect, but it has served me well and if you've ever tried to do a search on Linux instructions, you'll appreciate a manual which is complete and up-to-date.
Yip plenty of ram if you want a gui. I've got Mandrake 6.1 installed on the 486 Presario 64megs running WindowMaker. Any RH 6 based distro will run fine. The good thing about DSL is it can be installed on the hdd as Debian (i forget the varient). Its creator has now moved on to Tiny Core Linux and DSL is no longer being developed I believe. Here's the link anyway http://www.damnsmalllinux.org/
There's also a few 2 fd disk distros available as well.
SliTaz may be usefull too http://www.slitaz.org/en/about/index.html and http://en.wikipedia.org/wiki/SliTaz_GNU/Linux
You may want to read this too . http://linux.oneandoneis2.org/LNW.htm
Do keep us posted on your progress.
FreeDos, MSDos 7.1, Open/DrDos or a variant, one of the earlier NT variants (4 for example), OS/2? Tons of free software out there to keep them usefull.
Mind you if you're familiar with Linux it makes sence to go that route or FreeBSD as others have suggested.
Folk seem to be giving away NT4 CDs these days. It shouldn't be to hard to get hold of one along with booklet and installation code. I've been lucky enough to get two in the last month.I'd like to keep the computer as it was originally, just like a classic car.
I'd like to use Dos or Windows or OS/2, I'll just use linux if I can't install nothing else.
And I have the floppy disks for the Windows NT 4.0, it's just that the installer asks for the cd rom and I don't have it and my cd drive isn't working.
I can't imagine there being any problem with installing DOS! You just need to fix the hardware. If you have a broken computer you're going to have trouble with anything.I'd like to use Dos or Windows or OS/2, I'll just use linux if I can't install nothing else.