Upgraded to Mountain lion but Mail won't work

Question

I was having problems with my email so I figured I'd upgrade to Mountain Lion (I was on Snow Leopard) and that might fix it.
Installed it and when I launch Mail it tells me it needs to import my mail.
It goes through a whole process about 4 minutes long and then tells me the upgrade failed.
"An erro occurred during the upgrade. Click Continue to launch the Mail Import Assistant, which will help you create a new library and import your existing messages"
O.K., sounds good.
Except when I click Continue I get an alert saying "Your Mail Index has been damaged. To repair it, quit Mail.  Mail will repair the index the next time you open Mail. Your mailboxes and messages will be preserved."
Liars!
When I click the Quit button, I'm back to square one and the whole thing starts all over again.
I don't even see a Library folder now on my hard drive, but it's got to be there somewhere, right?
I would just pull off the old Mail folder and copy it to an external drive and try and import from there but I can't even do that.
Any help would be greatly appreciated.
Thank you.

Answer 1

I found my old mail ( did a search and got an alias icon which I clicked on and it took me to a folder I could not see otherwise) and tried backing it up onto my exteranal. The copy failed at the offending corrupted file. I moved it to the trash and launched Mail again. This time the import went flawlessly. Hurray for me!