Lost Admin Password and have No OSX Disc. Single User Mode Crashes.

My office has a Mac Pro that came with 10.5.6 I believe. They immediately ran bootcamp to run Windows XP exclusively on the machine. This was a few years ago and I was not at the company. In fact, nobody that used it is still with the company, and we do not know the administrator password. We also do not have the grey restore DVDs and we don't have an OSX disc that will allow the computer to start from the disc (via pressing "c" at startup). The computer will not boot into single user mode in order to work around the admin password: it stalls out opening extensions.kext or something to that effect. For whatever reason safe mode is also not working. I think they botched the install with bootcamp, because even after removing the bootcamp partition, the Mac Pro will not startup without holding the option key to select the only drive available. Yes, this machine it royally messed up and we're trying to set things right...

The good thing is that we need literally nothing that is on the computer. we can wipe it completely if needed. Is there any other way to get around the administrator password? We're trying to update the operating system to 10.7, but we can't get past the first step without the administraotr password.

Thanks in advance!