Combine rum and raisins in small measuring cup.
Cook on HIGH (9) for 1 minute or until cup feels warm to the touch.
In glass baking dish, cook butter on HIGH (9) for 1 minute or until butter is melted.
Sprinkle with graham cracker crumbs; lightly press into bottom of dish.
Layer chocolate pieces, raisins and rum, and walnuts.
Pour sweetened condensed milk evenly over the top.
Cook on MEDIUM (5) for 1 5 to 1 8 minutes or until lightly browned.
Cut into bars.