I'm not aware of cracks for BBC's iPlayer software.
You used to be able to spoof their servers into thinking that you were an iPhone, so they'd send you a mp4 version (which is easy to burn to DVD), but they've probably stopped that now.
My suggestion, if it's a big popular show, is to search places like btjunkie.org and thepiratebay.org, and find it there. It'll be much higher quality, and it'll be in a format that's very easy to burn to DVD.
(The Windows software for iPlayer has DRM, preventing this.)