No sound on Toshiba L30 Notebook

I have recently purchased a Toshiba Notebook which came with "Vista" preinstalled. After trying several Linux distributions I settled on Mepis because it recognised more of the notebook's hardware than any other distro. However, although Mepis seems to have identified the sound hardware I cannot get any sound from it despite trying every tip I found in this forum.
In the Windows Vista device manager the "Sound,video & game controllers" show the sound device as "Realtek High Definition Audio" with a driver of the same name. Realtek provide a Linux driver for download but I have had no success with it.
In Mepis the output from lspci shows:

Audio device: ATI Technologies Inc SB450 HDA Audio (rev 01)

All references to sound in the output from lsmod are as follows

Module size used by
snd_hda_intel 15768 4
snd_hda_codec 195760 1 snd_hda_intel
snd_pcm_OSS 37408 0
snd_mixer_OSS 14336 1 snd_pcm_OSS
snd_pcm 62856 4 snd_hda_intel,snd_hda_codec,snd_pcm_OSS
...
...
snd_timer 18308 snd_pcm
...
...
soundcore 7008 1 snd

I do not know what these things mean or whether they are relevant to the problem but the info may help.

The content of /etc/modprobe.d/snd-hda-intel is

options snd-hda-intel position_fix=2
options snd-hda-intel model=auto

I have tried commenting out the first of these lines but that seems to make no difference.

There is another file /etc/modprobe.d/sound which contains

alias snd-card-0 snd-hda-intel
alias sound-slot-0 snd-hda-intel

I have not experimented with this file and I suspect it may have been created during my fiddling with other things???

The only entry in /etc/modules, apart from comments, is

"fuse"

That's all the info that I can think of that may be relevant except to say that sound works fine with "Vista" but I hate using that, so I should be grateful if somebody could suggest how I might progress in getting sound from the Toshiba using Mepis.