Since NTFS support was added into multiman here is a step by step guide to getting your vendor ID and device ID.
First right click on "Computer" or "My Computer" depending on what version of windows you are using. Then select properties. You must login or register to view this content.
Second open the device manager this will also be different if you are not on windows 7. I believe the device manager is a button in windows XP. You must login or register to view this content.
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Third expand the "Disk Drives" tree and right click on the USB hard drive you want to use with your PS3. Then select properties.
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Fourth step is to click on the details tab.
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Finally you will need to find "Parent" in the drop down selection and copy the circled numbers into the "USB.CFG".
After this is done you need to copy the "USB.CFG" into "/dev_hdd0/game/BLES80608/USRDIR" on your PS3.
The last bit after 0x0000:x0000:X Where X is the volume number so if you plug in your hard drive and it has 2 partitions like G: and F: the this needs to be 2 or however many partitions it has.
Start up multiman get to the file browser hit Start + /\ plug in your UBS hard drive wait a bit then hit continue.