A computer can recognize a second partition on a USB hard drive only if it can read the partition. If computer is unable to read the secondary partition, the partition may be in an unsupported format ...
I seem to remember someone in either this forum or NTMojo being a guru with partition tables... I.e. if I told them what was on a drive that had a hosed table, they could give me the bits to hex-edit ...
There are some situations where you'll wish you had one.