All up to 2A should work! The charging process with 500mA could be slower. But they will all work!
Just calculate, the original battery has 3.7V with 900mA, that makes 3.33Wh.
So the charging process is never at full capacity for optimal charging of the battery.
With an output of 5V and 500mA the charging should last about an hour or 1 1/2 hours. So I think 1000mA should be more than enough.
Couldnīt find any hint on the original output current of the HTC charger, sorry.
Phone: HTC HD2
ROM-Version: 1.66.407.1 GER