Adding users with first.last name

[Chris]

Hi all,

Hope this is the right list :) 
I'm using Fedora Core 2, updated.

Is it possible to add users to the system using a first.last name
form? I get an error when attempting it: ' useradd: invalid user name
'john.doe'. I have to add about 800 names to a mail server and
shortened versions would have duplicates, I have an older RH 8.0
server that I've been able to add users with this user name form, but
I couldn't see any difference with any config that would allow it.

Thanks for any advice

-- 
C