I don't think ahulls suggestion will help, since windows doesn't generally recognize partitions on removable media.
You should be able to download jpeg images over USB without any problem using normal windows software. Downloading raw / DNG using standard software is a bit trickier. Whether it shows up over USB depends on the combination of prefix and extension you use for the files, and which combination works may depend on your camera. On recent cameras, the .DNG extension will never be visible. A combination like CRW_nnnn.CR2 is probably a good place to start. You can also try using the same prefix/extension the camera uses for movies. If you are actually shooting DNG, you will likely need to rename the files after downloading them. Finally, for the files to show up, you need to be sure the camera has been rebooted between taking the pictures and connecting the USB cable.
You can also download files using the chdk ptp extension:
http://chdk.wikia.com/wiki/PTP_Extension this allows you to download any file, but requires you to use CHDK specific software to do it, and may prevent you from using normal software to access the camera.
If your PC doesn't see the camera at all when you plug in the USB cable, this may be due to having the USB remote setting enabled.
