mount USB drive read-write but only got read-only so far

[Adam Hardy <adam.ant@cyberspaceroad.com>]

I have a couple of questions about mounting and writing to a USB drive.

I bought a 1Tb Western Digital 'Passport' HDD that powers itself from the USB, 
so just one cable to plug in. I want to use it to back up both my Debian box and 
my girlfriend's Mac which uses Time Machine.

I let the Time Machine back-up use it first and now I'm trying to put my stuff 
on it from Debian, but HAL will only mount it read-only.

First of all, can I use pmount myself to mount it read-write somehow?

From fdisk -l, I see my ext HDD is called /dev/sdc1. But when I do "pmount 
/dev/sdc1", I get a directory /media/sdc1 but it's empty. I tried it with sudo 
and same result.

It seems most people have other problems with Time Machine back-ups like just 
reading them at all or creating them, and I haven't found anybody talking about 
what I can do to share the hard drive with one.

And if I can mount it read-write, will it stuff the Time Machine back-up? I 
guess I can experiment, the back-up's not critical to keep at this time.

Thanks in advance
Adam