Cradoc
The Gnostics believe that EVERYTHING physical here on Earth is evil, hence matter, this includes our bodies and they believe that matter is a necessary evil we must pass through to reach heaven.
I believe, although I have not studied this extensively, that they view it more as unclean.
Gnostics, as far as I can tell; you can't find many to ask around these parts, see the spiritual as pure and clean. They believe that sin and things that are not pure are only possible in the material world; the world that has been tainted. I think it is to do with either original sin or something along those lines.
They strive to be as pure and spiritual as possible, but admit that everything material is tainted, and that includes them.
To be honest, this is not too distant to the teachings of many branches of Christianity. They see original sin as existant in all humans, or at least that all humans are in some way impure from either their past sins or the sins of those before them. All of their beliefs and dogma runs towards how to cleanse yourself and then stay clean.
The basic idea in most of these is that we are all unclean, and only by becoming more spiritual do we escape sin. The details may vary, but I think it is mostly semantics and dogmatic beliefs, not the actual core of the religion.
More relevant to this guild, here is a gnostic piece talking about creation and their own beliefs in that regard. I will leave you to it;
http://www.gnosis.org/genesis.html