Moving 2d Galaga style aliens

I`m thinking of doing a 2d shooter ala galaga.

My only slight sticking point is what method to use for moving the `aliens`

problem 1
- i`m thinking of using Beizer curves for the diving aliens..but need to align the angle of the alien with the bezier curve...ideas

secondly...
-best way to move aliens in circular movements (eg sins/cos,pre plotted routes etc)

Any ideas gratefully received

cheers

GP

Generate paths turtle/logo-style? Made a path-generator with that functionality once, worked like a charm..