it could definately be the alty fuze, and it could be a bad ground/bad connection somewhere. Check the fuze, and check all the connections you had off when you did the alternator, including but not limited to the battery connection, alternator big wire and little wire. Also look for anything that might be rubbing now that you moved a wire a bit.
however, I also say that DSMs(and other Japanese cars of this vintage) have a tendancy to destroy batteries when the alternator goes. And, on any car, when the battery is low due to a bad alternator, and you put in a new alternator and fire it up, the new alternator is going to go balls out to charge the low battery. It can take SERIOUS life off it, or even kill it in a few min of doing this. I have seen that at work and heard about it more often than you'd care to believe. You may have fried your new alty already.