For what its worth.....
I have had tremendous results using a vellum paper from SMR.
try this link and start reading:
http://www.smrsoftware.com/vellum.phpI use an HP 2600 color laser, set for recycled paper (I'm using Ubuntu 9.04, so you'll need to fiddle in Wyndurs), and I do spray a matte fixative after to "darken" up the toner.
My last board has trace widths < 5 mils. I printed to the vellum such that the toner side is on the copper during exposure. I was careful on watching the exposure and developer time. BTW I didn't need to increase exposure time from using transparent film, not at all.
An inkjet attempt should prove interesting
Compare the prices on this vellum to that of laser transparency film, yikes!