Hi Alyssa!
You need to enter stormfist castle from the underground. For this take a concentrated look to the sewers in ars magicana. If you are not sure where to look you could join the thieves guild and ask for some help.
Concerning the "murder of the duke" quest (completely different one) you should speak with Sir Dante in Verdistis. This could prove very helpful indeed... <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
