Recently I manually downloaded my podcasts to myApple Nano Ipod 8GB on another computer other than my own. Since returning to my own computer I have not been able to delete podcasts from my Ipod even though the screen within iTunes for podcasts does not show podcasts other than the ones I have downloaded as new items.

You must have your iPod set to manually manage. You will need to select the podcast menu on the iPod in iTunes, not the Podcasts section of the iTunes Library. If they still are not showing up you will need to use a smartplaylist set to genre is podcasts on the iPod to find them all. Hi-light them and press Option and Delete on a Mac or I believe it's Shift and Delete on Windows keyboards.