Hey, if you now a good welder or any of your friends do then get it welded :(.
However, i took my bike with a small crack in to somebody out of the paper :(
and the frame gave way within 2 days.
I think if you heat the frame up to much whilst your welding the frame it weakens the metal causing it to last no where near as long as it would if you just left the crack (i could be wrong).
So try and get some one who has been recomended by some one.
cheers andy