I have a backlog of all my favourite podcasts and i was wondering if I could speed up the rate at which they play to say 1.5 or 2.0 of the normal speed
This feature is not available in iTunes, but you can choose the playback speed on the iPod or iPhone. By playing it there and synchronizing back to iTunes, it will mark your backlog items as played.
If this podcast was created by you (or you have the audio file), you could try to use Audacity. Here's their description:
Audacity is an easy-to-use, multi-track audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems. Developed by a group of volunteers as open source.
Basically, download it, and then drag your file into the main window. Then select track > Cmd+A > Effect (menu) > Change temp (not rate) > Check Use high quality stretching (slow) > Adjust your rate > click okay. Then, export it (File > Save other). Chose your desired filetype, etc. Drag the file back into iTunes.
You'll also need to change the track back to a podcast, so right click it > cmd+i > Options > media kind > Podcast. It'll now be in your podcast folder.