virtual domains with postfix and cyrus - mail gets delivered to defaultdomain

I am trying to set up a virtual domain now that my postfix/cyrus setup
is working (many thanks to the guys on this group by the way). It is a
blackbox setup with no unix accounts. Not sure if this is a postfix or
imap question. Big dent in the wall where I've been banging my head all
evening!

My problem is that email to pete@virtual.dom gets delivered to
pete@my.real.domain (the default domain for the system).

I'm running on SuSE enterprise 9.
postfix-2.1
cyrus-imapd-2.2
cyrus-sasl-2.1

/etc/postfix/main.cf
########
######## VIRTUAL DOMAIN SETUP
########
virtual_transport = cyrus
#virtual_transport = virtual
virtual_mailbox_domains = virtual.dom
virtual_mailbox_maps = hash:/etc/postfix/vdomains

(I have tried a number of virtual_transport lines)

/etc/postfix/vdomains
pete@virtual.dom JUNK

/etc/imapd.conf
virtdomains: userid
defaultdomain: my.real.domain

The system appears to strip off the virtual.dom domain and send it
locally so it gets delivered via Cyrus IMAP to pete@my.real.domain.

The postfix mail log shows it coming in and accepting it for
virtual.com, but then it goes and deivers it as if it was an email for
the default domain.

I am also getting the following error:

May 19 00:00:20 ktinga postfix/virtual[8165]: fatal: bad string length 0
< 1: virtual_mailbox_base =
May 19 00:00:21 ktinga postfix/master[5127]: warning: process
/usr/lib/postfix/virtual pid 8165 exit status 1
May 19 00:00:21 ktinga postfix/master[5127]: warning:
/usr/lib/postfix/virtual: bad command startup -- throttling

I assumed that because I am handing the mail off to cyrus, there would
be no need for a 'virtual_mailbox_base' setting ?

I have tried putting

pete@virtual.dom pete\\\@virtual.dom

as I read on one site that this can 'trick' imap into receiving it for
the virtual.dom.

The virtual.dom account appears to be sound - I can log into it, copy
mails into it etc

The directory:
/var/spool/imap/domain/virtual.dom/user/pete/
exists.

Any thoughts on what I need to do do make postfix hand off to imap and
stick it in /var/spool/imap/domain/virtual.dom/user/pete/ would be much
appreciated.

Thanks guys.
Pete