Mailchimp first/last name field sync?

I have installed the mailchimp newsletter integration plugin into my BP site

WP 3.0.4
BP 1.2.7
none multi-site.

I am trying to sync the existing few members of my site with the list. The plugin has some help text saying that on syncing it updates 'the first/last name of previously imported users'.

I have tried a number of different field names for the name column in mailchimp but none of them seem to import the users username, first name or any name

can you please tell me what the mailchimp field should be called in order to map my Buddypress users name, username, first name - or whatever it should be.

Many thanks