Vista - Restoring Live Mail Messages from Backup - Most efficient way

Hi, Think I may have screwed up a little. Maybe I should have copied the
whole folder rather than export it then I could have just copied it back
possibly?. Right, had a system problem so had to restore my whole hard disk
from about a month ago. So now my mail is about one moth old. Fine because
before I restored the system I backed up by exporting all my mail accounts
messages contacts etc, which is of course up to date. I now want to restore
those messages into my month old WLM and am wondering what is best to do. If
I import will it just add these messages to the existing store which will
mean I have a significant number of duplicate emails? Will it overwrite the
duplicate emails which is fine as it will effectively just add the new ones?
Should I delete all the messages in the month old store and then just import
the up to date store. Before I do this I would like to know from an expert
the definitive answer. As you can imagine with a 1.2gb message store I dont
want to geyt it wrong! Thanks for your help. BTW will it maintain the
original date information of each mail?

Appreciate some expert advice!