Importing existing SSL Certificates into Plesk

[newgen]

We have various client's with SSL certificates on an existing non-plesk server running Windows 2000 and IIS5. We have exported the certificates using the export function through the certificates snap-in for the MMC, however we are unable to import the files into Plesk 7 for Windows 2003

Is there another way to accomplish this? Are we way off-base? We use this process to move client's between non-plesk servers frequently, however we are moving strictly to plesk and will have a large number of clients with this same problem.

Thank you in advance,

Lee