To tether over Bluetooth requires you to use the default Windows Bluetooth stack. This took me a while, searching various forums and what not, to get it to work. After uninstalling the Toshiba Bluetooth drivers, I had to use this post to edit the INF file to get the Toshiba hardware to be recognized by XP. After getting this working, the tethering setup was a breeze (guide 1,guide 2).
Unfortunately, the default Windows Bluetooth stack is abysmal, and doesn't support the A2DP Bluetooth profile, which is the Advanced Audio Distribution Profile, and what my Motorla HT820's use for stereo audio. These headphones include two profiles, one being the A2DP, the other being a standard headset. I had them working previously on the Toshiba stack, with both profiles. Even worse, is that the default Windows stack doesn't support headsets either! (I've used Bluetooth headsets with my personal laptop and a USB Bluetooth dongle for Skype and other such applications.)
Looks like I won't be using these headphones with this laptop anymore . . . bleh.
Of course, for completeness sake, I should mention these wireless headphones don't work with my iPhone either, as the iPhone doesn't include the A2DP stack either.