I want to be able to ride my mountain bike on roads, but the sound of the mountain tires on the road is annoying. Can I just buy rims that will fit cyclocross or road bike tires? My bike has disk brakes.
It looks like the Cannondale F600 mountain bike has the typical 26" mountain bike tires. It's very unlikely that the larger diameter ("700c") rims used on typical cyclocross or road bikes would work well. There are road bikes with 26" rims, typically made for shorter people (especially women and children), so it would be possible to find rims in that size (but would make more sense to simply buy new wheels than to build wheels with new rims).
However, you can buy smaller, thinner, smoother, higher pressure tires for a 26" rim, and that would solve your problem quite handily. It would also be much cheaper ($20-$50 per tire) than replacing the rims (or whole wheels).
Do you mean rims or wheels?
Many cyclists have a second set of wheels for their bike, because it's a lot cheaper than having a second bike. Buying a set of 26" disk brake wheels with narrow rims and putting slicks on them is a pretty common thing for MTB owners who commute on their bike. You might also choose a slightly higher-geared cassette for the road wheels. You will need a second cassette on the new wheel, and a second pair of disk rotors. Two complete wheels, in other words.
If you are talking about rebuilding your wheels with narrower rims that's expensive and I think pointless - it will not be much cheaper than getting a second set of wheels, and will limit your choice of offroad tyres. You can mount fairly narrow tyres on most MTB rims, especially on newer bikes as there's been a fair bit of work on making fat tyres work on narrow rims, so racing cyclists can have narrower rims (because they're lighter).
The cheapest option is to just buy skinny tyres, but that means swapping tyres every time you want to go off road. Which is why many riders buy extra wheels. Another cheap way is to get a second hand road bike (but be aware that that is a slippery slope and many of us have more than two bikes)