Welders - TIG <-> MIG?

[JAMES_S_WALLACE@HP-Canada-om1.om.hp.com]

     I have a neighbour who's upgrading his shop and has offered to sell me 
     his TIG welder. I don't know the price yet. It's a 120 volt light duty 
     model which appeals to me for now. I asked what the difference was 
     between MIG and TIG, and he told me that MIG is for aluminum and TIG 
     is for steel. May he have said that backwards?
     If it turns out that what he's got for sale is really for aluminum I 
     don't want it, so could someone let me know the real scoop?
     
     Thanks,
     Jim Wallace