-

Hi Sate,

If you've been reading this board for the last month or so you might have seen I've been posting a few messages about setting up (With Oxy/Acetylene) myself. I already have one very under-used Clarke MIG after I found it would flick the power off every time I started to weld almost. First you should check you have breakers (If you plan to do it at home) that won't trip with your machine if you decide to arc weld.
MIG (Metal Inert Gas here in the UK or GMAW, Gas Metal Arc Welding in the US) is excellent for anything that isn't too varied if you're not planning to spend much on a machine. Your machine will almost certainly have just a few current settings available and it'll take a little bit of practice to adjust your speed to get a good weld. You can just use straight CO^2 or like the post above suggests, CO^2 and Argon mix. Make sure you get one with a comfy trigger if you do because I suffer the tradgic finger wobble, because mines that bad, that cause the weld to cut when my finger lets go a little. After a while the welds are almost spatter free and can be polished up to shine with a wire brush on an angle grinder. Expect anything from $200 for a simple machine to $1500 for a nice one. Mine was about $280 and works fine for welding things like sheet and joints for tables and such.
Stick (Or SMAW, Sheilded Metal Arc Welding) is really a little confined for all the things you might want to do. It's not particularly clean and it's fairly uncontrolable compared to other methods if you're not too good at it. It is however, incredibley cheap, if not the cheapest type of welding equipment available. You can pick up really simple Stick supplies for not much over a $100. It's only called shielded due to the flux coating on the rods you'll use but they're no match compared to a gas shroud.
TIG (Tungsten Inert Gas, HELI-Arc as in Helium Arc, GTAW Gas Tungsten Arc Welding) is the real clean, precise way you can go if you have the money. If you're thinking about TIG you may as well aim to get a full AC / DC machine as well. You can buy DC only machines for no more than $500 without the accessories but they really are BASIC. With only DC you can not weld ferrous metals at all. It will still be a very, very good, clean weld. With AC though, you're free to weld nigh on everything. A good AC / DC machine like a miller Econotig is about $1200, then you need the gas on top of it. It's much like gas welding but incredibly clean!
Gas welding (Oxy/Acetylene) is especially useful if you don't have much equipment and need to cut sheet or plate, gouge or heat. It's very versatile indeed but very mucky, very dangerous and puts a lot! of spread heat into your parent metals. It's quite easy to warp and bend joints or metals while you weld. I did a weld along a piece of 6mm deep steel to 6mm steel and was amazed at just how long it stayed warm afterwards compare to things I'd MIG togther. I tried force cooling a weld in some water, a bad idea if you want the weld to be anywhere near strong, and unlike with the MIG the weld buckled voilently and split warping the parent metal. Like TIG though it's quite 'simple' in that you can independantly control the heat and wire seperatly, whereas other methods demand both heat and filler being controlled together. You can watch for the metal reaching the correct temperature then start the bead, and if it gets too cold, stop and heat again. Arc machines like MIG or Stick can not do this. It is not really the right thing for just welding your frame for your truck together but still I really can't say how useful I've already found mine after just a week or so. I've cut heavy plate in minutes, cut a table top for a school project and I plan to use it to weld the legs and fittings to it. You can expect to pay $200 to $700 for the set and $100 to $300 for the cylinders. I have two that come up to just above your waist, technical or what (I can give you their sizes if you are interested), that have lasted me a very good deal of cutting and are still fine while I'm practising welding.
I would say your proberly best getting a MIG machine for your truck. TIG would be even better if you have the money and Oxy/Acetylene if your going to be doing other things with it as well. I would suggest you don't get a Stick only machine. Many MIG and TIG supplies will power a Stick electrode if you require it. I would suggest you check with BOC, if you are in the UK, for the gas prices to ensure you can afford to keep the welding set running. Have a look for information on any sites you can find about what people have used different methods for and decide which is best for you.

Good luck and all the best,

John