Yea guessing this is your amp?
http://www.walmart.com/catalog/product.do?product_id=4541643
Looks like you are stuck, either put it to an 8ohm load and hope to feed the sub with 200w or see about getting a DVC 2ohm sub maybe? I would look to getting a different amp first though. The setup won't be reaching its potential but it certainly should do fairly decent though. I had a pair of Infinity 12" subs running off a Jensen 4 channel feeding them an optimistic 150w each in a sealed box in a trunk car and it was pretty decent sounding. I won't say it was loud as I never had it metered, but it would beat pretty hard in my opinion.
Least give it a try before you drop any more money, you may be happy with it and your unknowning friends may find it just fine.