Follow signs for the Auto Collections inside the Imperial Palace, this only gets you as far as the correct end of the hotel. Then look for elevator #9 and take it to the 5th floor where the collection is housed.
I like the look of classic cars but I could not see paying to walk through and see this collection, especially when they offer a free printable ticket on their website. It's not a big time consuming museum either. We took less than an hour to parooze the vehicles they had; lots of Mustangs and Rolls Royces, some for sale and some just to look at.