Peter,
We can help!
In the "Projects & Articles" section there's a couple of write-ups on DIY spectroscopes - a Classical and a Littrow.
http://www.iceinspace.com.au/63-339-0-0-1-0.html
http://www.iceinspace.com.au/63-500-0-0-1-0.html
The Astronomical_spectroscopy group was established with the sole purpose/intent of providing support and resouce material for the amateur spectroscopist.
http://tech.groups.yahoo.com/group/a..._spectroscopy/
Then there's "Astronomical Spectroscopy for Amateurs" -published by Springer (available through Amazon). Section three of this book walks you through the theory and construction of various spectroscopes.
IMHO the hardest part, and probably the most important part, is the slit and being able to effectively aquire and guide on your target star...
Hope this helps.