on win2k with 1.3.1
I think the differences might be due to different rehashing algorithms being used in Hashtable and HashMap.
Giving an initial capacity in my test significantly reduced the time and in all cases HashMap was a little faster.
Hashtable - no initial capacity - 220ms
Hashtable - initial capacity 150000 - 70ms
HashMap - no initial capacity - 210ms
HashMap - initial capacity 150000 - 60ms
These are average times over several runs.