Anybody have any info on using a mig welder in their garage? Do you need to get some kind of heavy cloth up? How easy is it to start a fire with the sparks? What about ventilation? Do welders create metal dust that will cover everything in the room?
X2 on what all else have said about dust and fire. I would like to add that the reason I have a fire extinguisher in my pic is because I caught my car on fire. The one in my build thread. The fuel line was cable tied tight to my floor that I was welding. The floor got hot enough from weld penatration to melt the cable tie which in turn melted the fuel line. That let the diesel out and leaked onto the concrete into a big flaming puddle 
Another thing, never weld galvanized steel indoors or without wearing a respirator, the zinc coating emits poisonous gas during welding.
Along with a welder, you will need other tools. A Matabo 6" grinder, A die grinder, (harbor Freight $29.00). Cut-off wheels for the grinder, accessory bits foe the die grinder. You will find these tools "worth their weight" so to speak.
Also you'll need those cool small stainless steel bristle wooden handled brushes various grades of sandpaper for prepping the work site.
I did an apprenticeship as a TIG welder mumblety mumblety years ago.
My first bit of advice is take a community college course which exposes you to all types of welding. Some people find they have a knack for one type or another.
There is no good all-purpose welding, they all have their advantages and disadvantages. A well rounded course will let you play with all of them, on someone else's gas and consumables to boot.
If you go for equipment look at used. Just about every type of shop out there that has metal in it will have some welders kicking around, and lots of them are on hard times and selling equipment, cheap. Some stuff like oxy/aceteleyne rigs haven't changed much in ages. Newer inverter TIG units are the bomb, you can look for ones that have combo setups that can do a few different types well.
^^ Good advice! I took a welding night class at the college where I was doing my trade schooling and I'm pretty sure I used up the registration fees in materials every night. It's a great way to learn or practice while learning a lot from people with experience.