hello Wilf,
using old carpet is fine as long as it is the type without the foam backing (hessian type) ,and with wool as the fabric not any man made type of stuff, ie nylon etc. You can cover the ground with anything that blocks out light in fact , such as cardboard, or the black plastic they use on farms for silage covering . It all depends on how 'green' you want to be....? The cardboard box way is likely the greenest and safest , although even that is printed with ink that may? be a bit iffy. Whatever you use it does work as long as you keep out ALL light , and it will only kill off the annual weeds , things like dock etc will pop up again if not dug out (been there done that !!!). I prefere to just dig from the start nowdays. All you need do is turn the top 4"-6" completely over so the grass etc is facing down . While you do this you can remove all dock etc from the turf. All other vegetation, will die off and then in spring the weed seeds will start to germinate, let them get about a week old then hoe them all off . Keep doing this till no more weeds pop up, then sow you veggie seeds. This way you end up with very few weeds growing till you re-dig the ground , you then bring up more weed seeds from below the surface and you do the same again , let them sprout and then hoe off. It is the first 2-3 years that are the worst for weeds, after that they tend to be less of a problem . Good luck whatever way you do it .
cheers
Russ