Doorguru,

Looked around the web and found this site for building your own spot welder....
http://www.5bears.com/welder.htm

And here's one from Miller..
http://www.millerwelds.com/pdf/Resistance.pdf

And finally Mig spot welding...
http://www.esabna.com/EUWeb/MIG_handbook/592mig11_1.htm

Hope this helps.

Wade