290 courses are seminars which faculty offer (and sometimes students along with faculty) on specific topics.  They change each semester and might be announced last minute via the espm-gradstudents list or just posted as posters in the halls of Mulford, so you should actively check to see what's being offered.

299 courses are research units; you *must* be enrolled for 12 units to be considered full-time, and if you are done with classes you'll need 299 units to fill out your 12 units.  Usually these would be done with your advisor, and they will sign off on them at the end of the semester - so, you should know whether they are the sort of professor who wants to see specific results or not - though the units are pass/no pass (satisfactory/unsatisfactory) so I'd imagine things would have to go pretty badly in order to not pass.  Each professor has their own code for their individual 299, so you'll need to get this number from Doty (who usually sends them out before registration time).