1. Install all the latest updates from Microsoft (see Resources for download links). This may instantly fix your DLL relocation error and will at least make your computer safer and more up-to-date.
2. Re-run Realtek HD Audio Control Panel or whichever program first gave you the 'Illegal System DLL Relocation' error. If the program runs properly without displaying the error, your problem is solved.
3. Download XP update KB935448 from the Microsoft Download Center website. This update is specifically made to fix the DLL relocation error and will take care of it if an automated update didn't resolve it for you. Click the 'Download' button, run the installer and follow the instructions.