30 minutes before preparing ice cream crust, put a 9" deep pie pan in freezer.
To make the crust: working quickly, line bottom and sides of frozen pan with ice cream. Do not put ice cream on edge. Build up crust 1/2" above edge of pan by overlapping tablespoonsful of ice cream. Freeze at least 2 hours.
Combine sugar, pumpkin, spices and salt in a saucepan; cook over low heat for 3 minutes. Cool. Reserve 1/4 cup whipping cream for garnish. Fold remaining whipped cream into pumpkin mixture. Spoon into frozen ice cream crust, swirling top. Freeze at least 2 hours.
In a small saucepan over medium heat combine brown sugar, butter and water. Bring just to a boil; cook 1 1/2 minutes, remove from heat and stir in pecans. Cool. Spoon mixture around edge between filling and crust. Mound the 1/4 cup of reserved whipped cream in center. Freeze.
To serve: Place pie in the refrigerate 10 minutes before cutting into wedges.