Move from Lenny and KDE to Squeeze and TDE

A few months ago, when my desktop turned its toes up and went skywards to its rest, I started to use my testbed machine as a temporary desktop. It was already running Squeeze and TDE, so I moved my mail folders and set out to use it. My emails simply wouldn't display, and when I installed Lenny on this machine I found that said emails had been mauled. Fortunately, I had three copies and the third was fine. So far, so good. Now Lenny has been pensioned off. (Well, will have been by tomorrow.) I clearly have to face Squeeze and TDE again. But I want my email; emails, folders and all. I can find no reference to anything other than what I did, and it is not impossible that the HDD was faulty and that that is the problem. I have searched on Google, but so far as I can tell, I did the right thing. So please, before I dive in again, and this time I would not be able to retreat to Lenny, can I have all and any advice on how to save my emails? Other than take a large number of copies, which I shall do anyway. Thanks, Lisi