Probably easiest to remove your sdcard, place in a card reader and mount it on your computer. Copy everything off into a separate directory on your hard drive. Then format the card if desired, use the default allocation unit size (8k) and fat32. Copy back the obvious folders, .android_secure, music, DCIM, Clockworkmod, wallpapers, licenses, etc. Do you have any apps installed on sdcard? If something doesn't work after re-inserting the sdcard, all the files are available on the computer to copy back.