Hi Newbie,
Check what Service Pack you are running. If it is not SP4 then you will need to install it.
SQL replication prior to this has trouble with really large transcations. I have recently had this issue with a large transactional replication.
Check this out for more information - it might not be the same issue as yours but it sounds like it could be:
http://support.microsoft.com/kb/884554
I hope this helps.
Darren