Going from relying on "the guy in the shop fit your wheels" and not knowing the correct term for "the bit for the chain to go round" indicates that you probably are not now ready to safely build your own wheels. Please note that testing your theory that "I'm not sure that I can be any more cautious than "having a go" on a wheel that is most likely destined for the dustbin anyway" is great way to end up in the hospital.

You're going to have to learn the proper bicycle component/parts terminology just so that you'll know what to purchase. You might also need one, or more, "specialized" tools in order to safely build your own wheels (this is not to mention that you're going to need an assortment of decent hand tools).

At this point, I'm going to say that, for you, your buckled rims are most likely junk. Rim "straightening" (let alone wheel building) is not something for an absolute beginner to tackle. It is, as others have mentioned, very important that you reason out just why your wheels are failing in only a few weeks. Just some of the wheel failure issues that must be addressed are: both your weight and the weight of any cargo you're carrying, the speeds that you travel at, and the type of tires and the air pressure(s) that you're running them at. Failure to properly address these issues will, almost certainly, result in further wheel failures (as others have previously mentioned).

I too strongly suggest that you start by thoroughly reading Sheldon Brown's repair guide:

http://sheldonbrown.com/repair/index.html

You should, imo, also read Park Tool's repair help guide:

http://www.parktool.com/blog/repair-help

The great thing is you've put at least two of the biggest "bicycle mechanic" hurdles behind you: i.e, the desire to work on your own bike, and the intelligence required to ask questions.

Have a good holiday season and a happy New Year!