I really messed up Mail, now how do I fix it?

Question

(Please pardon the long explanation)
Where I was:
PowerMac G4, running OSX 10.3.9, Mail 1.3.11
All working well.
Burned a back-up DVD of my Mail Library and preference files.
Where I went:
MacPro G5, running OSX 10.5.8, Mail 3.6
How I got there:
Started the brand new G5, ran through multiple updates, installed files from DVDs burned off the G4. From the back-up DVD, dragged the contents of the Mail Library folder and dropped them into the G5 folder Mail user's library. When a dialog box appeared, asking if I wanted to replace identically named folders, I clicked 'yes'. Dragged and dropped the preference files in the same manner. Internet access through Airport, and Safari work just fine, happily.
What happened:
When I first opened Mail, a dialog box said it needed to input files from previous Mail or something, after about two minutes, it opened, showing the mailboxes from the previous Mail in the G4 (Yeah!). Within twenty seconds, an alert requesting the mail server password appeared, and ten seconds later, Mail crashed.
Where I am now:
When I open Mail now, it opens showing no previous mailbox folders, then quickly the dialog box asking for a password appears, and seconds after, Mail crashes.
What I think happened:
I most likely messed up by mixing old files into the new system. Looking at the Mail folder now, I have no idea what is corrupted and what is good. There are some duplicates by name. Deleting some of them hasn't helped.
What I want to do:
Re-install a new Mail system, get it working, than input all my old mail from the G4 in some fashion.
I would like to have all my email from the last five years on the new system.
Questions: How can I fix the mess I have now? How can I get a fresh Mail system, and then transfer the previous emails from the G4?
Thank you sincerely, Isshi.

Answer 1

Isshi wrote:
1) Can I import my previous signatures by dragging and dropping in the Signatures.plist file, or do I have to re-write all the old ones? The file in the new Mail is named SignaturesByAccount.plist so it's named differently.
2) Can I import the previous address book somehow?
3) How can I import the filter preferences?
4) Do I really have to re-construct all the mail mailboxes in the new system (now they are nestled in the 'import' mailbox)?
Despite my earlier suggestion I'm not an expert in mail importing, so others will have to contribute their ideas on some of your questions. Here's what I can tell you regarding your first two questions:
1) I'd avoid trying to use that Signatures.plist file. I agree that it seems to be organized differently from the earlier version.
2) Address Book can import an "Address Book Archive". I'd go back to your 10.3.9 system (if you still have it) and see if you can create such a thing.