How can I import and embed a .cptx file into PowerPoint 2007?

Did you want to embed it as a playable video file, or as images/text on each slide?  If it's as a video, you can publish the project as an MP4 and you should be able to embed that on a PowerPoint slide (or use a convertor to convert it to a video format that will play within PowerPoint.

If you wanted the images and text, you could publish using the Print setting in Captivate, and select the Handout option. This would give you a Word document with a screenshot of each slide, and all the text that appears on the slide. You would then have to copy and paste the images and text you wanted into PowerPoint.