freebsd stable - Mar 2005 - 5.4-BETA sysinstall seems to want to write to its own / instead of the one on disk

I've just put together a new box and tried the 5.4-BETA1 bootonly iso. The
box
has one SATA drive ATM, it has a Intel D925XECV2 mobo with onboard SATA. It 
does newfsk the disk but when it wants to write to it either when setting up 
users/groups or installing packages or distribution sets it folds:

/: write failed, filesystem is full

It seems to be trying to write to its RO memory disk? FYI I set up the hard 
disk pretty normally with an /, a swap, a /tmp, a /var and /usr and /home 
partitions. It did complain about geometry but I get that often. I could 
newfs and fsck it through sysinstall, so I think it's not a device problem.

Installing 5.3 then cvsup to 5.4 and make world worked fine. 

I can test stuff on this box if folks want to.

Dan