I have made a fruit beer before. Not a big fan of the flavoring, I have had some store bought beers and did not like them. If you want to add real raspberries to your pot just steep them for 10-15 min at 150 degrees at the end of the boil. Adding the raspberries should drop the temp to around that, depending on the amount you use. The store bought ones should be fine, 4 or more pounds should be a good start.
And dont forget to attach a blow-off tube, you will need one !