[Dovecot] mbox vs maildir

[poohba at blkpoohba.dyndns.org]

I am a little confused and maybe if I figure this out I will be able to 
get this to work.  I am now able to get my pop3 working but not imap.  My 
inbox is in /var/spool/mail/%u and my mail directory is /home/%u/mail and 
then all the 'folders' are there which are actually files.  Is that 
maildir or mbox?  Which do I have to use for dovecot?  Or can I use 
whichever I choose.  I would like to keep the setup I have and use IMAP 
but i am finding this very difficult.  I find some places that say I have 
to convert what I have and other places that say I don't.  Can someone 
please break it down for me.