Forget the TC-DC58D, it's overpriced and rarely available 2nd hand. Go for the older TC-DC58B 1.5x and couple it with one of the generic Chinese copy adapters, make sure you get the metal 2 part one though. You can put this together for about 25 quid. This is what I use on my G12 and it's excellent

HTH. When you attach it, don't use the menu setting that tells the camera you have a teleconverter attached, leave it set as if no converter is present. All this does is bump up the EV to compensate for a slight loss of light and you'll wind up with overexposed images.
Also note that you'll only be able to use the converter at full or very close to full zoom as it vignettes really badly at anything less. This applies no matter what brand/combo of adapter and converter you use.
One more thing, don't buy the copy teleconverters like Raynox or unbranded ones, they're rubbish, stick with the genuine Canon ones and only buy the ones that have the letter suffix, ie; 58B,58C,58D etc. These are much better than the ones that don't have the letter.