Mac OS X 10.3.6: "Peter Chin
To all that were having calculator problems: I was able to get Calculator to show the Basic window every launch (its normal execution) by deleting ~/Library/Caches/Calculator and ~/Library/Preferences/ com.apple.calculator.plist. Do this and then relaunch Calculator and this should fix it.
It was interesting to note that ~/Library/Caches/Calculator was only re-created after I updated the currency rates. Little Snitch told me that Calculator had tried to access an Apple address and the International Monetary Fund."