Check out our MegaSquirt thread on the forums.
http://www.mr2australia.c./mr2play/tm.aspx?m=18242 I need to update it with more information with regards to the DIYPNP, MS3PRO (just came out this week) and some other information.
The best place to pickup a MegaSquirt of any forum (MS1/2/3, DIYPNP, MSPNP or MS3PRO) is DIYAutoTune (
http://www.diyautotune.com/catalog/index.php) If you can swing a soldering iron, the DIYPNP is probably your best option as it is cheap, but has a lot more onboard hardware then a normal MS1/2 which makes it easier to get things off the ground (relay drivers, knock sensing, sequential injection (with a $30 plug in board), sequential ignition).
If you find electronics are confusing and you grab the wrong end of the soldering iron repeated, then a MSPNP is probably your solution, however you will need to talk to Matt/Jerry @ DIYAutoTune to see what is your best option.
To use a DIYPNP, I think the Toyota 76 pin one will cover the 3SGE (
http://www.diyautotune.co...embled-kit-p-384.html)According to my google foo, the 3SGE runs a 26, 16 & 22 plug setup. Which will work with 3 out of the 4 sockets on the 76pin setup

You would just plug into the 26, 16 & 22 sockets with your loom connectors.
If your at the MR2 Challenge, feel free to come and see me, my AW11 runs on a DIYPNP and I've done a couple of installs using the DIYPNPs and MS2's so I can probably give you some information and maybe a wiring diagram or 3 :)