I have a variation on this problem and I'm also seeking a solution. For years I ran Windows XP on Parallels 3.0 Boot Camp on my Mac Book Pro with OS 10 (Tiger). Because everything ran just as I liked it, I resisted making any upgrades. Then some expensive hardware problems necessitated me buying a new Mac Book Pro with Snow Leopard. I was able to keep the original hard drive from my first machine in an inclosure as an external drive so I can import data and apps from it via USB. But I’m having a hard time with Parallels.
As I feared, Parallels 3.0 will not run with Snow Leopard, so I bought the upgrade to version 5.0. I've installed it on my new Mac Book and installed Windows XP fresh from the original installation disk. But I'm struggling with the transporter tool and I'm at a loss as to how to import anything off my old Parallels 3.0 which lives on my old drive (now as an external USB drive). It's showing as winxp.hdd, taking up 65 gigs of space - I'd love to access some of my old software, documents, pictures, etc.