If you are working in a DV project, the preview will be DV (which is not a good compression for graphics), but that won't affect your final export. If you want to keep the same quality in your previews, you will need to work in a desktop mode project, which will force a render to uncompressed.
Yeah, Vince is right. The preview can be deceiving.
Also, you'll want to check how Camtasia is compressing the video. I've found rendering out of Camtasia as an uncompressed AVI is generally easiest for Premiere to swallow (although it yields massive files). The proprietary Tech Smith codec Camtasia uses by default in rendering AVIs tends to cause problems working inside a DV project.