if you are taking the wheels with the tires, it should fit. but you can not take those 25x11x12 tires and put them on your wheels you already have. i had to look at what ITP has listed for these too machines...ill do my best to explain what i am talking about so you understand. your machine has a 25x11x10 tire. this means when mounted and inflated to the proper PSI, your tire is 25 inches tall, 11 inches wide, and has a 10" diameter for the wheel.
Xplorer/Sportsman 500 4x4, 96-08 (R)
25x11x10 10x8, 4/156
now we get into wheel sizing. 10x8 for the wheel means breaks down like this. 10 is the diameter of the wheel, and the 8 is the width of the wheel. no offset is listed, so we can assume there is no offset, which wold make the wheel a 4+4. so you wheel reads like this: 10x8 4+4 4/156. the 4+4 means you hub bolts to the wheel dead center of the wheel. if it was a 5+3, it would mean the hub bolts to the wheel inch over center of the wheel towards the outside of the machine. and finally, both rims are a 4/156 bolt patter, which means there is 156 mm from center of one stud to the center of the other stud in a straight line.
Sportsman 600 4x4, 03-08 (R)
25x11x12 12x7, 4/156
so the tire from the sportsman 600 is the exact same physical size as what you have now, except for it has a smaller sidewall since it has a larger wheel diameter. the rim is a 12x7 so this wheel has a bigger diameter, but is 1" narrower then your current rim. since again, no offset was listed, it should be a 4+3 offset. which reads that from the inside of the wheel to where it bolts is still 4", but this rim has 1 less inch on outside of it, so if anything, the total package will give you a 1" narrower wheel base on the rear, from each wheel. the thing i would be concerned about is if it happens to be a 5+2 offest. you can measure this with a tape measure to find out fore sure. the reason i am concerned with the 5+2 wheel base is because with this offest, when the wheel gets bolted to the hub, there would be an extra inch of wheel and tire on the inside, and i am concerned that extra inch will cause rubbing issues on the shock and strut. but, being a 12 inch rim with a wider opening, that might not be the case. a 4+3 offset should be golden though. and the bolth pattern is still a 4/156 so no worries there.
did i help? or did i confuse you more?