I just recently ordered Lemmings off of E-bay, and the game failed to open on my XP computer, even with compatability enabled. So I tried it on my older '98 computer, and it worked, but only after rebooting. I rebooted it again (accidently leaving the Lemmings disk in), and the computer tried to boot off the lemmings disk. It failed (of course), but in the process, the lemmings disk was corrupted or something, I don't really know. At first it seemed like the files were just erased. Now I only have half of my files I think, but I can't be sure because I don't remember what other files were on the disk. I checked on my XP computer and it thought that the disk was still at full capacity, even though most of the files won't appear and can't be found. So I ran a recovery program and it found some fragments. However, I still can't install Lemmings, because my files are still missing. I was wondering if anyone could...
a) help me with the problem, maybe say what went wrong, or something. The instruction book says I should return the disk to Psygnosis, but I'm pretty sure they're out of business. If anyone has the same problem or knows what I can do to fix it, that would be great.
b) write up a list of files that came on the disk so I know exactly what I have and what I'm missing. The files that I have on the disk are:
Help.bat
Ground3O.dat
Ground2O.dat
Ground1O.dat
Ground0O.dat
CGASpec3.dat
CGASpec2.dat
CGASpec1.dat
CGASpec0.dat
CGAMain.dat
CGAGR4.dat
CGAGR3.dat
CGAGR2.dat
CGAGR1.dat
CGAGR0.dat
ADLIB.dat

I think that the ones I'm missing are the copy-protected files.

You can download, for free, all the relevant files--in fact the whole game basically--from abandonia.com.

As for the game not running properly in XP, that's known and to be expected since XP no longer has any remnants of DOS around.  You can either run it in Windows 98 as you did, or you can try running Lemmings under DOSBox 0.63 in XP.

Kudos for buying it instead of just downloading it!

But yeah, DOSbox is the way for XP. DOS lemmings w/o DOSbox seems to run very slowly on my PC, and without sound.

Any file that might be corrupt can be replaced with the files from http://www.tecotronic.com.br/dados/Progs/XT/Lem/ or http://mensa.familia.rebello.nom.br/dados/Progs/XT/Lem/
The site's slow, but the files are dated as being from '91.  Some of the files seem to have been added tho.