The few times I accumulate these they swept into my AA account at 8 GP/mile so assuming you joined the at as a Radisson member ( and not at say the TGIF Gold points which give a different exchange rate) 20k GP = 2500 miles which about equals 2500 Starpoints. You sholud be able to figure out the HH equivalent but I would say 1 starpoint = 4 HH points.
mike