Here's what you have to do, Slightly Disoriented:
First of all, open a terminal window (Applications -> Accessories -> Terminal), then type the following command to see what device your USB drive is:
Then, zero out the USB drive:
sudo dd if=/dev/zero of=/dev/sdX
where /dev/sdX is the full device (not any partitions) on your USB drive (i.e. /dev/sdb, *NOT* /dev/sdb1). Unlike previous commands mentioned, this will erase *ALL* data on the *ENTIRE DISK*.
Next, you can use GParted to create a new MBR and partitions for the flash drive.