try putting the phone in usb debugging mode. then select from the drop down menu(notification bar) to connect via usb. It will take a few seconds to connect and the little green droid robot will pop up and there will be a button at the bottom to push to connect. Once it connects the robot will turn from green to orange.
you should get 2 drives show up. the sd card and the usb internal storage. On my phone, i had already named my sd card, so that name came up and the internal usb storage on the phone came up as "no name". so if you havent named the sd card, be careful in which drive you select as its possible both will come up with "no name". You may be able to tell the difference by the drive size if your sd card is bigger or smaller than the 16gb of onboard phone storage.
usb debugging mode is under menu>settings>applications>development.
Leave the usb cord unplugged from the phone, select debugging mode, then plug the usb cord back in and follow instructions above.
Once youre done doing what you need to do with the internal storage and the sd card, turn off usb debugging mode.