Hmmm,..Hajo, I know it might be a silly question, but did you install the stuff from the Creative CD's? Or did you just install the driver from the WEB site?
Here is a trick most people miss. The WEB drivers Creative has are updates and check for the installation of a previous driver from CD. However, you do not have to install the CD drivers. If you put the CD into the drive you installed Windows XP from, the WEB drivers will look there for them and then install.
This makes for a very pristeen installation.
Also note if there were any remnants of the SBLive driver laying about, it can cause problems.
As a side note, the Audigy 2 ZS I have, made a remarkable improvement in everything I run. All games got better frame rates and ran smoother than they ever did with the SBLive card.
I don't use VIA based motherboards, as a side note, so your mileage may vary.