I have ALi M5451 souncard in my laptop (Compaq Presario 900z for those 
searching) and it hangs the machine with any kernel I tried 
(currently 2.4.20-ac1 + hirofumi patch). I traced it down to the line 
where it hangs - that is drivers/sound/trident.c:3379 which says:
pci_write_config_byte(pci_dev, 0xB8, ~temp);

removing this line fixes the problem for me.
I am not sure what would be the proper fix.
The hanging looks slightly different at different times: sometimes it 
would just freeze, but sometimes it would would start giving ide 
errors on any operation and sometimes it was giving this message:
"i8253 count too high! resetting." once or twice, but anyway the 
system was not functional after that.
I got similar results with alsa drivers for this card, but I did not 
debug that.

I am also getting several IRQ conflict messages on boot, I wonder if 
that could be related to this problem and I wonder whether they are 
something I should worry about or not.

Fedor

PS. some additional info about the system in case it is relevant: it's 
Compaq Presario 900z with Athlon XP 1500+, lspci output is attached, 
distribution is debian unstable.