this one will do it.
http://www.homedepot.com/webapp/wcs/...ctId=100093231
I would use .035 inner shield wire (no gas) to weld a frame.
BUT !! if you are new to welding, it would not be smart to weld a frame together. If the welds fail people could die. Have someone that has good experience help out on that.
A more powerful welder would be the best thing for a frame but that little one can do it, its the operator that will be the variable.