I have never been "married" in the temple, but I have been "sealed" twice. First to my wife that had passed away and the second time after we had been married civilly for five years.

My question is; is there a difference between the "marriage" ceremony and one that is only a "sealing"?

well, you are married anyway. One is supposidly for eternity, however.

I guess I am wondering. Is there a separate "marriage" ceremony before the sealing? Is there a "I Do" part for lack of a better term?

Not in the USA. Here you get married in the temple, if you don't, you have to wait a year to go through and get sealed. In Europe, the government doesn't acknowlege religious weddings (you have to be married civilly before and religious wedding) , so the church lets members there get married civilly, then get sealed the same day.

married / sealed are a bit interchangable. If you go through the first time it's getting married (and having your relationship sealed to that it will last through eternity). If you didn't than you basically go through the ordinance so that your family will be together.

Nope. Pretty much exactly the same. Mormon "weddings" are everything except a marriage ceremony. Prophetess Normarae says that's going to change soon.