>I teach a high school math course and we have been working
>on fermat primes, unmarked straightedge and compass
>constructions,and so on. We've trisected given angles with
>a marked straightedge, enabling us to construct regular
>7-gons and 9-gons. Now we are wondering if we can
>"quinsect" a given angle with a marked starightedge and
>compass. Answers, hints, and indications in the right
>direction are welcome.

I highly recommend Geometric Constructions by G. E. Martin. The book tackles constructions by compass and straightedge, compass, straightedge, marked ruler, dividers, sticks, paperfolding, and some more.

There is a Gleason's Theorem (p 141):

A regular polygon is constructible with the marked ruler iff the regular polygon is constructible with the tomahawk.

(Tomahawk constructions are equivalent to compass and angle trisector constructions.)

In particular, 7-gon is constructible with a marked ruler whereas 5-gon is not.