You almost certainly want a MIG then. If you're doing anything MIG related you really want a decent (Speedglas) auto helmet, just read the welding helmet posts on this forum if you need any convincing - it makes the job sooo much nicer and the results so much better. If you want to weld for more than 5 minutes you'll need to rent a bottle of Argoshield from BOC as the disposable bottles are akin to using five-pound-notes as a shield.
To weld anything a bit heavy you want more than an el-cheapo hobby MIG, and the bigger the unit the nicer it should be when doing anything else. I'll defer to all the adults on this forum who know what they're looking at as I just bought a big old 200A industrial welder from Jez (one of the Stig's hand-me-downs I think) so bypassed having to look at any of the hobby stuff. If you don't mind something big, heavy and aesthetically challenging then a used industrial unit can be a good bet, although single-phase stuff fetches a bit of a premium. Does give you more space for pimpin' graphics and neons later on though
IMHO a euro-torch is a huge plus (although the conversion kit only costs £40). Get the longest torch you can and a really long earth lead, and a clamp type earth connector not a jumplead style one.

To pass off others' advice as my own - don't buy a full size reel of wire as it will go rusty before you've used half of it, I buy the half-reels (well, I've bought one so far) and that has done a hell of a lot of the 109 and isn't showing signs of running low yet.