Is there I way to tether via BT from my phone to my computer?
Yes. You'll either need a USB dongle or have it built into the computer. It's basically the same as tethering with a USB cable, except that in the dialup connection's settings you need to choose the BT DUN modem instead of the 'standard modem'.
PS - Don't install any of the software that comes with the dongle if you are using XP/Vista. You have to use the built in driver stack, in order for DTM to pair via BT.