5.2-BETA boot failure

I tried upgrading a Dell Optiplex GXa from Release 5.1p10 to the 5.2
Beta using the mini-install CD.  The system hangs in the boot loader. 
This problem doesn't happen with the Release 5.1 CDs.

I then tried upgrading from source after getting CURRENT as of
11/29/2003, and was able to build and install the new GENERIC kernel.
Upon reboot, the system hangs in the same way as when booting from the
mini-install CD.

The only thing unusual about this machine is that the onboard EIDE
controller is disabled, and a PCI EIDE controller has been added.

The system doesn't seem to get far enough to get a dmesg output or a
backtrace out of this, but here's a transcript of the last few lines if
it helps.

Timecounters tick every 10.000 msec
ata2-master: WARNING - SETFEATURES recovered from missing interrupt
ata2-master: WARNING - SETFEATURES recovered from missing interrupt
ata2-slave: WARNING - SETFEATURES recovered from missing interrupt
ata2-slave: WARNING - SETFEATURES recovered from missing interrupt
ad4: WARNING - SETFEATURES recovered from missing interrupt
ad4: WARNING - SETFEATURES recovered from missing interrupt
ad4: WARNING - SET_MULTI recovered from missing interrupt
GEOM: create disk ad4 dp=0xc23ce960
ad4: 19541MB <Maxtor 52049U4> [38703/16/63] at ata2-master UDMA66
ad5: WARNING - SETFEATURES recovered from missing interrupt
ad5: WARNING - SETFEATURES recovered from missing interrupt
ad5: WARNING - SET_MULTI recovered from missing interrupt
GEOM: create disk ad5 dp=0xc23ce660
ad5: 4121MB <Maxtor 90432D2> [8374/16/63] at ata2-master UDMA33
ata3-master: WARNING - SETFEATURES recovered from missing interrupt
ata3: resetting devices ..

machine is hung at this point.