2001 Tacoma frame is not particularly thick and an AC stick welder can be difficult to use for something so delicate.
The main issue is that it's easy to blow through the metal or to create a weld that is not strong enough to handle the stress the frame is under. When you're welding, you need to make sure the crack is properly prepared first by grinding it out into a V shape. Gives better penetration of the weld. However, a small crack on a frame can be an indication of a larger issue, so it's a good idea to have it looked at by a professional if you can't do it yourself.