When I was doing some intarsias, I finally figured out a fairly fast way to convert the line drawings into vectors.
1. The intarsia pattern I purchased from Judy Gale Roberts Studios, I took to FedEx Kinkos and had it scanned and saved as a pdf file.
2. I imported into Photoshop, changed it into grayscale and inverted it. Adjusted the levels slightly, erased parts of the images I didn't want and saved it as a tiff file.
3. Imported it into Aspire and did a trace bitmap, then exported it as a dxf file.
4. Dropped it into Adobe Actobat X Pro and saved it again as a PDF file.
5. Took it back into Photoshop to save it again as a tiff file, so I could imported back into Aspire.
6. Back into Aspire, the image now is very crisp and did another trace bitmap. The handful of flaws was corrected in node editing. The patterns now are already separated, so there's no need to offset if it was just a single line.
Although the picture shown is not totally complete and still needs a little editing, the total process of taking into the various software programs only took 5-6 minutes.