Welcome to the forum! The only water in ID that I have fished is the South Fork of the Snake but it is a big river, better suited for drifting, but if you're in the area I wouldn't let that stop you from trying a couple likely looking spots. The river flows along hwy 26 from Swan Valley to Idaho Falls. When driving west along hwy 26 after passing Swan Valley look for N. 175th Rd and follow that north until it crosses the river and then turn right, it will turn into a dirt road, follow that east along the river, there are a couple of Y's, stay to the right to follow the river, the road will turn into Burns Creek Rd and lead into BLM land and watch for likely looking spots to fish.
Do a search for Dorian.Ducker and then send him a PM, he is a member and lives in Idaho Falls and he should be able to point you in the right direction. Same goes for idahoflyfisher and bigcabindana (he lives in Twin Falls).
You might also pick up a copy of Fly Fishing the Henry's Fork by Mike Lawson and Gary LaFontaine:
Fly Fishing the Henry's Fork Mike Lawson Gary LaFontain - eBay (item 350319528522 end time Mar-22-10 05:25:40 PDT)
This is an excellent DVD by Mike Lawson on the Henry's Fork: