Poor texture mapping with fabrics

Hi all,

I'm having an issue with texturing fabrics. They look pretty good in the work window, but when I render, they look nothing like they should, but rather a series of large boxes with each box having a series of streaks. So a textured panel, for instance, looks normal in the work window, but very distorted in the render. I've played with the 3x3, 4x4, etc. filters, but nothing. I'd upload some samples if I knew how.

Thanks.