At Chelsea (it's the 2nd traffic light), turn right onto M-52. There may be construction through Chelsea.
Continue north on M-52 through Stockbridge until you get to I-96. (NOTE: to get thru Stockbridge: Turn right at the stop sign just past McDonald's, then left at the next stop sign by the town square.)
Take westbound I-96 until it intersects with US-127.
Turn right onto northbound US-127 and continue on this road through Lansing/E. Lansing. (This part can be tricky as there is a lot of relatively crazy merging and stuff. Just don't take any of the exits. Liz adds that it's best if you can kinda stay in a middle lane.)
North of Lansing, US-127 becomes US-27. Continue on US-27 until Houghton Lake. (There is about a 20-mile stretch of US-27 -- between St. Johns and Ithaca -- which is NOT limited access. Also, there may be construction in the Clare area.)
When you get to Houghton Lake, take the M-55 exit and turn right.
At the 1st traffic light, turn left onto Old US-27.
Turn right just past the bridge over the Muskegon River. (There is actually a street sign that says "Muskegon River".)
Turn left at the 1st stop sign -- you will see the lake right in front of you.
Continue on this road until you get to a stop sign -- just past the Four Seasons store (on the right). Again, the lake will be right in front of you.
Turn right onto Long Point Drive. The cabin is at 445 Long Point Drive and hard to miss. It's on the left and there are two camping trailers in the yard ;-)