error messages from Adaptec driver when installing system

[Steve Kotsopoulos steve@ecf.toronto.edu]

system: IBM PS/ValuePoint, 486DX 66MHz, 8Meg, Adaptec 1542CF, Seagate ST11200N

I'm trying to load Plan9 onto a PC (still waiting for the CDROM), but there
are long delays and error messages related to the scsi controller, then
it eventually panics:

1268 free pages, 5072Kbytes, swap 32592K, highwater 252K, headroom 312K
CPU is a 26MHz 486DX (cpuid: ax400 dx0)
scsi0: aha1542 port 330 irq11, dma 5
fs...time...adaptec0: timeout cmd=#00
adaptec0:invdcmd #02, len 1
adaptec0: timeout cmd=#03
adaptec0:invdcmd #02, len 1
adaptec0: timeout cmd=#1b
adaptec0:invdcmd #02, len 1
adaptec0: timeout cmd=#03
[snip]
/fs 13: serving #s/dos
registers for fs 14
FLAGS[snip]
panic: divide error[rest omitted]

I can fill in the details I omitted if they would help.

Questions:
1. Why is it reporting I have a 26MHz 486DX instead of 66MHz?
2. Is something wrong with the Adaptec, or something else?

FYI, here's part of the boot message from BSDI on the same system:
vga0 at isa0 iobase 0x3c0 maddr 0xa0000-0xaffff
aha0 at isa0 iobase 0x330 irq 11 drq 5: Adaptec AHA-1540CF/1542CF rev B0
aha0: extended BIOS translation enabled
aha0: delaying to permit certain devices to finish self-test
aha0: parity, bus transfer 5 Mb/s, bus on/off 11/4 us