If you find a friend with one of the newer versions of Altium Designer, they can directly import PADS files and save them to Protel99SE format.
If you would like, I would be happy to help you out. Just zip or RAR a copy of the file to protect it and PM it to me. I should be able to get a Protel99SE version of your file back to you within a couple of hours after I get it.