Mountain Biking - Help upgrading crankset

I'm looking for some info on upgrading a SR Suntour XCC-170NP, 24/34/42 crankset with something better. After the disaster with an LBS holding my brothers bike for 2 weeks to replace these cranks I figured I would venture on here in hopes that someone could point us in the right direction. We both are still learning about mountain biking so the lack of understanding what would work correctly is still a bit foreign to us. The cranks are from an '07 Diamonback Coil EX which is a starter bike my brother is using. The Shimano cranks on my Jamis are great and would like to see my brother use them but I don't know if any of them would work. Any help would be great. Thanks in advance.

I can't tell from a google search what kind of interface it has, but I'm going to go ahead and say now that it WILL work.

Don't pay an LBS to do this, the internet is you friend. For the amount of money you'd pay them, you can buy the necessary tools. Also, it won't take 2 weeks :D

If they are both ISIS or octalink or outboard, then all you have to do is swap the cranks and can leave the BB. Since one is shimano, it's probably octalink, and since the other cranks are cheap, they're probably ISIS.

Here's what you'll need
8mm Hex
Crank extractor (I hope you can get one to work for both ISIS and octalink)
bottom bracket wrench (or one of the hook/pin things).

Remember as you sit on the bike, for the BB cups, the Right side is reverse threaded (righty loosey, lefty tighty)
while the left side is standard threads (this is the opposite of how the pedals are threaded onto the cranks).

Take the bolts out of the center of the cranks, use the crank extractor to thread into those holes, and tighten it down to pull off the cranks/arms. Then remove the BB using the tool, remembering how the cups are threaded.

Take the shimano crank over to the other bike (which you've done the same thing to) and reverse the steps. It's worth putting some grease on the BB threads, and the BB splines, it helps with creaking.

Thanks for the reply but I'm a little confused, after re-reading my post let me specify that The shimano cranks I have on my Jamis are nice but they aren't being removed to put on my brothers bike. I was more interested in what cranks to purchase in order to replace the crappy ones he has. Also how difficult/cost effective would it be to change everything to a more standard setup. (ie: change from an 8 speed to a 9 speed setup)

You can't go wrong with Shimano cranksets. I'm not sure what your price range is, but the integrated crank/bb LX/XT work well and are reasonably priced. If those are too expensive, the Deore crankset is may be a good option. For a non-integrated crankset, you'll just have to make sure your existing bb is compatible with the crank (square tapper, octalink, etc.).

How to remove/replace various cranksets:
http://www.parktool.com/repair/byregion.asp?catid=59&imageField2.x=17&imageField2.y=7

Deore crank is like 65.00
not bad, its my next upgrade

you can run 9 speed on the crank you have now. I would say don't upgrade it until something breaks. If you want to go 9 speed you need:
chain,
cassette,
shifters

If you look around you can probably do this for $100-150, and it's at least as good of an upgrade as a (cheap) crankset.

You can't go wrong with Shimano cranksets. I'm not sure what your price range is, but the integrated crank/bb LX/XT work well and are reasonably priced. If those are too expensive, the Deore crankset is may be a good option. For a non-integrated crankset, you'll just have to make sure your existing bb is compatible with the crank (square tapper, octalink, etc.).

How to remove/replace various cranksets:
http://www.parktool.com/repair/byregion.asp?catid=59&imageField2.x=17&imageField2.y=7

My thoughts exactly.