Idaho Wilderness Boundary Modification Act of 2008 - Adjusts the boundary of the Frank Church River of No Return Wilderness in Idaho to include and exclude specified lands.
Authorizes the Secretary of Agriculture, in order to resolve the encroachment on the land designated for exclusion, to sell the land (and up to 10 adjacent acres) for fair market value.
Requires the person buying the land designated for exclusion to pay: (1) asociated appraisal costs; and (2) any associated analyses and closing costs. Gives the owner of the adjacent private land the first opportunity to buy the land.
Sets forth requirements for the disposition of the cash proceeds from a sale of land. Prohibits deposited amounts from being subject to transfer or reprogramming for wildland fire management or any other emergency purposes.