Looks like I'm too late to contribute to the pannier discussion*, but you don't have to resort to using p-clamps if your frame lacks the upper mounting points. You can use something like this- http://www.amazon.com/Sunlite-Bicycl...eat+post+clamp.

*I normally caution people about possible heel strike, but it is my understanding that the Nashbar atb mount up a bit higher, so that shouldn't (hopefully) be a problem for you.