I have seen this on other Dell Studio XPS8100 ... the resolve is simple and leads me to believe that Dell had a bad image on some these units... You can try these steps and decide for yourself:
Uninstall realtek drive (select the delete driver box when uninstalling) then delete the realtek folder.
Go to dell and download realtek audio driver and program R24528 (will be the same 6.0.1.5953 driver)
reboot and reinstall realtek software and driver -- I think your problem will be resolved
now try Express Scribe 5.03 and setting up Dragon Naturally Speaking ... both should now work
Good luck!
Please post back if this worked for you - Thank you