first Id like to say Im not an EXPERT at welding but have done quite a bit over the years
now just to answer some basic questions, heres some info from a differant site you might want to know!I'll try to cover some of the basics for you as best as I can explain them.
http://www.alpharubicon.com/elect/tigbasic1.htmTIG - (Tungsten Inert Gas Welding)
basically resemble oxy-acetolene welding (torch) but you use a controlable electric arc as the flame/head source, ans add the weld wire, or rod seperate from the arc 
This process is the toughest to learn. The electrode is composed of Tungsten, and a current is flowed through it controlled by either a foot pedal, a hand switch, or a fixed current on the machine itself. I am learning TIG using a foot pedal, the more you press down on the metal, the more amps you get. Once you get enough current flowing to get an appropriate sized weld pool, you start dabbing a filler metal into the puddle as you move the electrode further down the work piece. TIG allows you a great amount of control because you regulate how much current the electrode gets and how much filler metal the weld pool gets. This process is very slow compared to the other types though.
MIG - (Metal Inert Gas)
mig is basically a wire thats fed constantly into the weld area that got current running thru it, it melts both the metal and itself as its consumed/melted by the arc
http://www.autobody101.com/articles/article.php?title=Mig+WeldingMIG is the easiest process of welding. A feeding gun is used to feed a spool of filler metal wire into the weld pool. Current is usually switched on and off by means of a trigger on the gun. Amps are usually controlled by a dial on the MIG machine itself, meaning that you cannot adjust current in the middle of welding. Though, with some machine you are able to get a foot pedal to control Amps while welding.
Arc Welding
[b] these are the cheaper buzz box welders we all tend to start with, they use an arc thru the weld rod some what similar to mig but without the gas shielding, they have flux on most rods to help the weld quality[/n]
Arc welding is mostly used in industrial applications. An electrode is used to strike an arc, the electrode then melts away to deposit metal into the weld pool. The electrode is coated with a variety of different materials which are used to help keep the weld pool from being contaminated.
TIG and non-flux-cored MIG both use a variety of different shielding gases to help keep the weld pool from being contaminated depending on what metal is being welding.
http://www.stockcarracing.com/techarticles/82101/http://www.ytmag.com/articles/artint153.htmhttp://www.popularmechanics.com/home_improvement/tools/2001/3/welding_basics/http://www.hobartbrothers.com/aboutus/downloads/BTW, welding without the correct helmet is stupid, protect your EYESITE
http://www.thetoolsource.com/thetoolsource/scripts/prodView.asp?idproduct=26[url]http://www.maxtool.com/cgi-bin/dbsearch.exe?mdb=\tools.mdb,dbTYPE=2000,tbl=IC_ITEMS,template=/comp_master-3.htm,DBCOMP=ABS,dbsort=retail,ReturnMax=25,DB_CAT2=Whelmets[/url]
http://www.weldingdepot.com/?source=overturehttp://store.weldingdepot.com/cgi/weldingdepot/scan/fi=products/st=db/sp=results/co=1/sf=category/se=Welding%20Helmets%20-%20Auto/op=eq/nu=0/bs=1/ml=15/tf=description/to=x/se=1/sf=inactive/op=ne/sf=tax_category/se=1/op=eq/va=banner_text=/va=banner_image=.htmlhttp://www.brwelder.com/indexTemplate.cfmjust some info
THE MILLER WELDERS that REQUIRE a 230 volt feed have proven to be easier to use in my opinion than some of the cheaper brands,(YOU GET WHAT YOU PAY FOR) you can OCCASIONALLY GET GOOD DEALS ON E-bay on NEW and used welders, stick with the better name brands, accessories like wire feed guns and repairs are very difficult to get for some off brands. buy a welder that rated at at least 50% duty cycle or you could be constantly having it overheat on large jobs, or not have the power to do the larger jobs
http://www.autobody101.com/articles/art ... %20Weldinghttp://www.hobartwelders.com/weldtalk/
