Well... if you did not have a BDC to promote to a PDC, and so you just rebuilt the PDC, you're out of luck unless you have a backup good copy of the old registry. If you do, go to the MS site and download the procedure. It's not trivial, but it will restore all your security hives and, I believe, the SID for the domain. You will probably need NTFSDOS Professional, unless your WINNT directory is on a DOS partition, as you cannot copy the security hives back to the server while it is booted. You need to copy them over before you boot the server.
If you don't have a backup then you will need to re-add all the machines to the domain, and you may need to re-establish rights.
Good luck,
Walter