can it fit?
 

I got a Mongoose XR100 as a gift. i was on a trail, one thing lead to another, now the rear rim is a huge S.
since i need to get a new rear rim, i was going to get a new front one. (got to be matching), i was looking at rims and saw front disk brakes. I have only seen Disk brakes on real mountain bikes, rather then cheaper ones. If i get a new hub (front) to go with the new rim. can I fit a disk brake on the stock fork? it's a Element Racing fork. I know there will be some work in installing a disk brake on a V brake bike. But can it be done on stock fork, or would i have to replace it?

Firstly like Rayin said it would cost a lot more. But its possible. Not sure about the fork you have now, but if there are two sort of 'hole' connections down the bottom right i think, then it should be compatibal. Also you will need a compatible rim/connection that you would fit the disks onto. After all of that you have to purchase the disks which are quite expensive depending on what quality you want. Then you have to get 2 new wheels, so I assume the price would be A LOT cheaper, if you just went out and bought a new bike!

Yep, your best bet is to replace the wheel and stick with vees or get a new bike.