Does anyone know how to transfer email .mbox files from an old XP drive to a new Windows 7 one?

I have years worth of small business emails on my old XP drive. Everything is organized by customer and there are many hundreds of mailboxes in folders and subfolders. I rely heavily on the records there. So I MUST preserve them.

They were on an XP Pro SP3 drive, but it’s getting flaky. showing occasional errors on the boot sector, and XP is an abandoned dinosaur now, so it’s time to move to Windows 7. I have Windows 7 Ultimate installed and humming along on a new terabyte SATA drive, I can boot into either operating system. But the two operating systems have very different ideas about the folder structure where they store library files like mailboxes, email settings and address books.,

I installed my email client on the new Terabyte drive under Windows 7 and tried copying the contents of the mailbox folder from the old drive to the folder where Windows 7 puts its mailbox files. But this doesn’t work. The email client must build internal pointers as it works, and it apparently builds them differently in XP and in Windows 7.

I can’t use syncing programs because I can’t run them across the two operating system partitions. Any ideas on how to resolve this short of setting up a permanent partition and living forever with outmoded XP for email?