I've installed Debian Sarge onto my laptop, everything seems to work except for the sound. I installed alsa and ran alsaconf, and it seemed to detect my soundcard OK. There was even a 'pop' noise from the speakers. Here's the output it gave me: (thought I'd use two colors to distinguish my post from command-line output)

Unloading ALSA sound driver modules: snd-intel8x0 snd-mpu401-uart snd-rawmid-seq-device snd-atiixp snd-ac97-codec snd-pcm-oss snd-mixer-oss snd-pcm sner snd-page-alloc.
Building card database...


Running update-modules...
Loading driver...
Setting default volumes...
Saving the mixer setup used for this in /var/lib/alsa/asound.state.
/usr/sbin/alsactl: save_state:1194: No soundcards found...


===========================================================================

Now ALSA is ready to use.
For adjustment of volumes, use your favorite mixer.

Have a lot of fun!

But when I try to run XMMS, I get:

Message: device: default

** WARNING **: oss_open(): Failed to open audio device (/dev/dsp): No such fileor directory

And sure enough! ls /dev | grep dsp reveals that /dev/dsp does not exist. I'm using a 2.6 kernel. Here is what lsmod gives me:
lsmod
Module Size Used by
snd_atiixp 21640 0
snd_ac97_codec 69988 1 snd_atiixp
snd_pcm_oss 55080 0
snd_mixer_oss 20096 1 snd_pcm_oss
snd_pcm 98728 2 snd_atiixp,snd_pcm_oss
snd_timer 25732 1 snd_pcm
snd 57156 6 snd_atiixp,snd_ac97_codec,snd_pcm_oss,snd_mixer_oss,snd_pcm,snd_timer
soundcore 10336 1 snd
snd_page_alloc 11752 2 snd_atiixp,snd_pcm
ipv6 264740 8
ds 18756 2
af_packet 22568 2
irtty_sir 9152 0
sir_dev 19244 1 irtty_sir
irda 197120 2 irtty_sir,sir_dev
crc_ccitt 2144 1 irda
pcspkr 3592 0
rtc 12760 0
8139cp 20672 0
shpchp 101900 0
pciehp 99020 0
pci_hotplug 34640 2 shpchp,pciehp
ati_agp 8652 1
yenta_socket 21728 0
pcmcia_core 70868 2 ds,yenta_socket
8139too 26112 0
mii 5120 2 8139cp,8139too
tsdev 7392 0
ehci_hcd 32004 0
mousedev 10476 1
joydev 9984 0
evdev 9600 0
usbhid 32224 0
ohci_hcd 21764 0
agpgart 34664 1 ati_agp
nls_iso8859_1 4032 1
nls_cp437 5696 1
vfat 14656 1
fat 46784 1 vfat
capability 4520 0
commoncap 7232 1 capability
quickcam 121224 0
usbcore 119012 6 ehci_hcd,usbhid,ohci_hcd,quickcam
videodev 10016 1 quickcam
psmouse 20360 0
ide_cd 42656 0
cdrom 40732 1 ide_cd
ext3 127240 1
jbd 62616 1 ext3
mbcache 9348 1 ext3
ide_generic 1408 0
ide_disk 19296 4
atiixp 8920 1
ide_core 139940 4 ide_cd,ide_generic,ide_disk,atiixp
unix 28756 240
font 8320 0
vesafb 6656 0
cfbcopyarea 3872 1 vesafb
cfbimgblt 3040 1 vesafb
cfbfillrect 3776 1 vesafb

I'd be very grateful for any ideas or suggestions.

This sort of problem has been beaten to death on these forums. Do a forum search for something like 'debian sound alsa' and you'll come up with a ton of suggestions. Here's a thread to get you started. That's certainly not the only one, or perhaps even the best for your situation. It's just one that I know where to look for.

Heh, yes, I came across another thread where you made the same suggestion to another person. None of the fixes seem to apply to me though. Here are the contents of my /etc/modules file:

ide-cd
ide-disk
ide-generic
psmouse
videodev
quickcam

As far as I can tell, the i810 driver isn't being loaded. I've made sure I'm in group audio. As I understand it, the modules that start with snd_ are from alsa? Perhaps my sound card simply isn't supported... in lsmod, I have:

Module Size Used by
snd_atiixp 21640 0
snd_ac97_codec 69988 1 snd_atiixp
snd_pcm_oss 55080 0
snd_mixer_oss 20096 1 snd_pcm_oss
snd_pcm 98728 2 snd_atiixp,snd_pcm_oss
snd_timer 25732 1 snd_pcm
snd 57156 6 snd_atiixp,snd_ac97_codec,snd_pcm_oss,snd_mixer_oss,snd_pcm,snd_timer
soundcore 10336 1 snd
snd_page_alloc 11752 2 snd_atiixp,snd_pcm

I can't tell if this means the driver is working or not. (for my full list of modules, see the first post) According to discover, my soundcard is an ATI Technologies Inc IXP150 AC'97 Audio Controller

I'll fight with this some more before I admit defeat.

Looks to me like your sound card should be working. Have you turned up the volume? Have you gone in to xmms preferences and changed your driver to alsa? What exactly is your output from alsaconf?

For alsaconf output, see first post. I don't think it's a problem with XMMS, surely /dev/dsp needs to exist before any program can access sound? I found a bug report that says alsa's atiixp drivers won't load + create /dev/dsp with kernel 2.6.8 - my problem exactly. Also, alsa just has a big question mark next to atiixp on their compatibility page.

I'm going to try compiling alsa from source, rather than using the debian package. If that doesn't work, I'll try upgrading my kernel version.

Thanks for the advice, I've not given up yet!