[peepeesea]

when you plug your phone in via USB it should pop up and ask you what to do. Connect to PC screen on the phone. it has options like Charge only, HTC sync, USB tether and Disk Drive. Select Disk drive and then your SD card will show up in your My Computer as a removable drive. if the Connect to PC screen doesn't pop up you need to go in to Settings>Connect to PC and check the box next to Ask me.

to browse files on the phone download Astro file browser or any other file browser from the market