Thanks for the suggestions guys. I thought about the filtering, but the way the way Garda proposes isn't practical bacause a lot of those emails eman little to nothing to me without the names attached.
As for the second option, I haven't checked the import function in thunderbird itself, but from what I've read it supports comma or tab seperated fields. The structure of the file simply looks too complicated to me (I'll try anyway when I get home) it's like a list of code explanations at the top something like
followed by some of those fields being filled in for some of the email adresses
in addition all the accented characters (ñ, á, etc) look something like $a$n etc. What a mess!!
And then there are all the home addresses, telephone numbers and other details... I never thought I'd need to back all of that up
I sure will next time (or so I hope).