I got my OG about 9 months ago. Motorola came out with some new drivers within the last couple of months that work a lot better on my XP based PC.
USB and PC Charging Drivers - Motorola Mobility, Inc. USA
What drove me crazy was that I had to switch "on" USB on the phone before the drive would be seen. I saw plenty of references to it on the boards, but no instructions.
You have to slide down the notification bar (which is across the top) with your finger and choose and turn on "USB Storage" before the SD card is recognized by the PC as a drive.