Here is an interesting article on the Weld Pak 100 which Dave mentioned...

http://popularmechanics.com/home_improvement/tools/1997/8/lincoln_welder/

I was surprised at the 15 amp rating...

One thing to consider when looking at what sometimes are called " cracker boxes" is the duty cycle...

I have had my 250 amp Miller TIG machine for 35 years... and it had to have been 20 years old when I bought it... very heavy .... and 100 percent duty cycle....

But some small machines say to let them cool after welding a certain amount of time... I have heard of some with cycles of as little as 20 percent...

Which means you weld 2 minutes and are supposed to let it cool for 8 before welding more... however I also know people who say that they ignore the cooling period... since I have not had any experience with other than my 100 percent duty cycle machine I do not know if that is wise or not....

Notice also that the specs say up to 12 guage metal... this may mean lots of structural stuff can not be welded with this machine.

If you don't have an Oxy-acet outfit I suggest you get that first.... I find gas welding of sheet metal easier than stick. There are advantages in certain places and positions in which stick sheet metal welding reduces the amount of heat injected into the area... sometimes very important...

Another thing... get a CO2 fire extinguisher.... this will help a LOT... the seal on these works so that you can use a little at a time in the shop... and leaves no messy stuff like the powder ones....

Often times combinations of things are stronger than what one thinks of initially for fixing areas.... and this has been talked about before.... flanging, cutting holes, using rivets to keep in place, and plug welding into the holes ( which are only in one of the overlapped pieces of sheet metal ) have been proven ( where applicable ) for sheet metal repair.