It took about a day to get Gnash built and more or less running on OpenSolaris. Surprisingly few dependencies are missing, but the ones that are (mainly the Boost C++ libraries) aren't that easy to build.

So the packages I needed to build were:

1. bazaar (for retrieving Gnash trunk)
2. bjam (for building boost)
3. boost 1.37
4. AGG 2.5 (Anti-Grain Geometry renderer)
5. libgif