they were probably talking about using the "clark" as the power source for the attachment. As for spot welding with the mig gun, no promlem,. If you are spoting panels ie.. body panels, sheetmetal, make sure you space your spots out or you will end up with a warped mess.

 

You can also use a plug welding approach with a regular MIG welder. Drill a series of holes (3/16", 1/4", etc.) along the seam edge of the top sheet, then lay this piece on the partner. Use a MIG welder to build up the "missing" material in the holes. This will fuse it to the bottom sheet and to the sides of the holes you drilled on the top sheet. It's not exactly a spot weld, but it doesn't require any special equipment and it ends up being pretty close. The plug welds can also be ground smooth without worrying about removing too much of the bond between the sheets. Air-driven flangers with a hole punch on the other side are reasonably priced and easily set up the plug welds.

 

I think I might give this a shot. I really am not going to be doing enough to justify a special attachment.

 

Dog,
Vette Gator is on the right track.

see this ESAB link:
http://www.esabna.com/EUWeb/MIG_handbook/592mig11_1.htm

What is not shown in the ESAB link is the "spot weld nozzle" such as shown in the following link. The stand off feature of the nozzle allows the nozzle to be placed in contact with the sheet surface, holding a constant tip-to-work distance, and allowing shielding gas flow.
http://daytonamig.stores.yahoo.net/spotweldnozzle.html