To hold or not hold CTRL down

If I drag the bottom right corner of a cell while holding CTRL down, the contents are COPIED in my Excel 2002. However, if I do the same in my Excel 2003, the contents are incremented. I think there must be a toggle switch somewhere that decides which happens.
Where is the control for that ?

Originally Posted by davesexcel

Shift........

I'm perplexed - SHIFT by itself does not change the pattern I have described. Nor does SHIFT
in combination with CTRL..
To rephrase - I suspect that in Tools; Options; is the appropriate place to allocate the effect that CTRL will have when moving a drag handle, but I can't find a candidate.
Yet the discrepancy is real - my Excel 2002 behaves one way, but 2003 behaves another way !