Access 2007 unusable over network

Access 2007 seems to have severe (severe!!!) performance problems with
mdb's 
over a network. Over VPN it's downright unusable. It doesn't matter if the

mdb is upgraded or not... and it happens on both XP and Vista and on 
different machines. I expected the Office Suite SP1 to address this issue,

but it did not. This must be a known issue, no? Is there a workaround?
(no, 
we're not upgrading to ADP or going to use replication).

Access 2000,2002,2003 all work great.