Vectorize

1. Scan the drawing. For me, 300dpi was high enough resolution.
2. In Photoshop, I adjust the levels to bring out the black and kill the light grey. Save as .PSD file

3. Bring it into Adobe Illustrator CS2. Select your image, now select Object > Live Trace > Tracing Options.
To see the vector preview I always zoom in on a section of the image beforehand to be able to see the upcoming preview.

Mess with your options (more below)... then hit "Trace".

Blur - adds a Gaussian blur that can help reduce noise. Can smooth out rough edges.
Fill Trace - not stroke trace
Path Fitting - determines how closely the vector version will resemble the original image. Lower will keep jagged edges, higher will even them out. (setting the view option to compare original file and vector tracing helps a ton)
Minimum Area - determines smallest are to trace.
Corner Angle - sharpness of the angles in degrees.

4. Select the object, now Object > Live Trace > Expand
5. Optional / I always delete the outer white area by selecting it with the Direct Select tool (hollow/white arrow) and hitting Delete.

6. Save it as an .EPS file - or whatever your printer takes - and there you have it.
Hit up the image below to see a large before and after version.