Darren, as Rob said and...
Here are two other calculators you may like to use to calculate all aspects of the WHEEL, (diameter, offset, backspacing) as well as the TIRE (diameter, thread width, overall width, and height of the sidewall). It also is an EASY comparison of what you have and what you may want to use... and what will work! Click on the tires to see not only a side by side comparison, but also an overlay.
http://www.rimsntires.com/specspro.jsp
Using this calculator and measuring at least TWICE can save you a lot of time, frustration and MONEY!
This other calculator is an easy reference to speedometer correction, as well... if you choose to go with a different diameter overall.
http://www.tacomaworld.com/forum/tirecalc.php
I personally run a 205/60x13 in the rear and compared to a stock 165/70x13, there is a savings of about 100 rpm at 4000 rpm indicated... or a -2.6% error in the speedo. Compared to the popular 185/60x13 there is a -4.6% error or about 170 rpm reduction at speed, giving you a bit quieter cruising, if that is what you want.
Both calculators will also determine whether you simply need spacers and longer studs or if it would be better/wiser to go with an adapter.
IMHO... If I needed to go with an adapter I would look into a more conventional 4 x 100 or 4 x 110 bolt circle which would open up a PLETHORA of available wheels and options for you. (4x98 to 4x100)
AND, if you decide you don't like them... you have a much larger market to sell them.
HTH...