This camera should work in iMovie 11. It should also work in iMovie 09, but there are some special gotchas if you have both SD and HD recorded at the same time. http://support.apple.com/kb/HT1793
Here are some things to try.
1) Is your footage an an SDHC card? If so, it is easier to import from a USB card reader (or some current Macs have built in card readers)
2) If you don't have a card reader, you need to connect the camera via USB cable. The camera must be plugged in to wall power (not batteries only)
3) Check the Sony manual for the correct setting for import. Usually you would set the camera to Play mode, but your manual would say for sure. (You don't have to worry about this if you have a card reader.)
4) Check your version of iMovie. The current version is 9.0.4. If you have anything earlier, run Software Update.
5) If it still insists on opening iPhoto, open the Image Capture app and set the camera to not open anything.