Much as I'd like to run mine on a picaxe I have to say megasquirt is the way to go - like this forum only for efi. All the info you need is there, you build and tune it yourself, great fun learning.
I have used it on a 90cc single (3 fuel maps) a 2 litre Ford and now a 4.6 litre V8 (Cadillac Northstar). The web abounds with people who have done it.
WB 02 is worth the little extra cost, I found that my ears and nose were no substitute for reality and that the engine would run from about 9:1 up to 17:1!!
Radiogareth- It's amazing what Bruce Bowling and Al Grippo created through an open source community. I remember the diy-efi days. I haven't been keeping up with MS or VEMS(which, at least at one time, was far superior). Autos were a fun hobby for lots of years, then they became a burden. Now, I've just about lost all interest in them.