Podcasting - mic and headset help

I'm trying to get started with some podcasting but I'm not sure my mic and headset is up to the job.

I have a USB plantronics set that I use for Skype.

When recording Audio I'm using a couple of programs - Audio Hijack Pro, Audio Recorder and Audacity.

The quality is not great so I'm wondering if I need to upgrade my mic/headset. Is USB really suitable for decent quality recording?

If anyone could suggest some audio equipment that would be great.

thanks