After, well, years I guess, of trying whenever I stumbled over my Discworld II CDs, I've just successfully installed Discworld II with working sound on Windows XP. Most of the info came from this forum - I just improved on the solution in this thread, thanks Bouchehog. I wanted to write down how I did it for myself and then thought, why not put it here, maybe it can help somebody else. So here is what to do:

+ download the files disc.txt, vbeplus.exe and univbe.exe

+ rename the downloaded file disc.txt to disc.bat

+ run disc.bat in the command line while the Discworld II CD is in the drive, this installs the DOS version

+ edit the DW2.bat file in the Discworld II folder created by the installation:
at the end is written dwb or dwb.exe - add two other filenames before this to make it look like this

vbeplus.exe
univbe.exe
dwb.exe

+ put vbeplus.exe and univbe.exe into the Discworld II folder

+ download the patch for Discworld II

+ unzip the patch and replace the DWB.exe file in the Discworld II folder with the DWB.exe file from the patch-folder

+ download VDMSound 2.10 from here

+ install VDMSound 2.10, taking care to restart the computer before using it (maybe better read this guide)

+ set the sound:

- right-click on SETSOUND.exe in the Discworld II folder and select 'run with VDMS',

- the VDMS configuration wizard opens, select 'Use a default configuration', click OK

- You can check 'remember my settings' before clicking finish or not, read the description the wizard provides for more info.

- a DOS-window opens, choose 'select and configure digital audio driver', press enter

- select 'Creative Labs Sound Blaster or 100% compatible', press enter

- select 'Attempt to configure sound driver automatically', press enter

- select 'OK', press enter, select 'Done', press enter, close the window

+ choose the settings for VDMS and run Discworld II:

- right-click on DW2.bat in the Discworld II folder and select 'run with VDMS',

- the VDMS configuration wizard opens, select 'Set up a custom configuration', click OK

- select 'Create a new configuration from scratch', click OK

- click 'Advanced', the Advanced VDMSound Properties dialog opens

- on the register card 'Compatibility' check 'Enable low-level CD-ROM support'

- on the register card 'Soundblaster' choose '1.05 (Soundblaster1x)' under the heading 'Enable Soundblaster emulation' - 'DSP.ver.'

- click 'OK' to save the settings and close the Advanced VDMSound Properties dialog

- click 'forward', then check 'remember my settings' and click 'Finish' and

. . . enjoy Discworld II

To start the game at a later time use the VDMS-shortcut 'DW2.bat' created at the last step. You can play around with the VDMSound settings for Discworld II by right-clicking this shortcut an choosing 'properties'.

I tried different Soundblaster-settings and the described one (Soundblaster 1) got the best sound, but maybe there are other settings that work as well or better.