Shame windows based didn't work, I've had no problems with win7, Ext2 Volume Manager and the external HDFoxT2 drive here.
Linux is easiest via usb pen drive,
however, if both the Humax and Vista are connected via network then I think you should try the custom firmware on the HD-FoxT2 first, you'll need HD_FOX_T2_1.02.29_mod_2.19.zip
if you can't find it below then you'll need to google for it
http://wiki.hummy.tv/wiki/Firmware_Downloads
make sure you download the right version, install it onto the Humax, it's a bit trickier than the HDR-FoxT2 to install and once finished you should be able to mount/map the attached Humax drive with windows explorer using the ip address of the humax to your vista pc and with even more luck you should be able to write to it. If you can't and you can record a couple minutes of tv to it then it's looking like vista is causing the problem.
What I don't understand is if you can record a couple of minutes to the drive when attached to the Humax quite why you can't write to it when attached to vista with Ext2 volume manager.
If the vista and humax aren't connected via network then put something like ubuntu onto a usb pen drive, boot your vista pc into linux and you should be able to see both the attached usb drive and your vista partition and copy whatever you want across.
If there are still problems then let us know how far you got, I think important to know would be are they networked and can you record tv as normal onto the drive when connected to the HDFoxT2