exchange 2010 upgrade

hi

when doing the upgrade from 2007 to 2010 can you get the new exchange 2010 system running along side 2007 still live, then move owa over to 2010. Will users be able to access the new owa while there mailboxes remain on the 2007 in till i get a chance to move the mail boxes over or iis it a case when owa is moved over you then have to moved the mail boxes and other services before any can access and send mail again.

In theory the two should be able to co-exist - or so I am told by numerous MS documents and books. However, as you may have read I am having issues. This may not be the case for you as you're going from 2007 to 2010 which are very similar I understand.