mounting old PGP Disk volumes on my Mac

I have a few old PGP Disk virtual volumes from an old Windows XP machine (about 10 yrs old). I'm running a trial of PGP Desktop 9.9 on a Mac running OS 10.6.8 and trying to mount them. When I do, it says "no secret key found." All I really want to do is mount the old disks and copy over the data. I know the passphrase, but I'm not sure what software I need to do the job. Please advise.