iMac Not Recognizing Blackberry Tour to Sync

[macfan]

I had an old imac (the one that is a round dome with the flat screen attached).  When I attach my blackberry tour to it with the usb cable, it does not recognize it and show the icon on the desktop.  I tried updating the pocketmac software to the most recent version, but that did not solve the problem.  Can anyone help me.  I just purchased the Tour and would hate to have to return it.