You cannot dual wield two different classes of weaponry; in fact you might not even be able to wield different types. I'm not sure, but I believe the GI articles stated that you can only dual wield the same types of bladed weapons, so if you have one steel longsword than you can dual wield another steel longsword, or two glass daggers, etc.
I could be wrong, but I definitely know that you can't dual wield a sword and a mace.
Actually no. It doesn't say you are restricted like that in anyway. It actually says the opposite. They even have a screenshot of a guy duel wielding a one handed staff and a sword.
Here is this little excerpt for you "[...}Duel wield with two of the same weapon, or place a dagger in one hand and a mace in the other." page 50.
There you go. OP, you could use both if you want to go all offense.