Can they cast spells or conjure?

i would say no.

they can pretty much give orders, and that's it.

What he said. Without channeling you order the spirit and are just along for the ride. If you tell it "kill those people" it does so in a method it chooses; you can no more micromanage what powers it uses on what enemies in what order than you could if you'd given the same order to any other spirit.

could a mage project, while possessed? never been clear on that.

I think not. However, he could project and then tell a spirit to possess his empty body. The spirit could run around causing havoc while you do astral overwatch or whatever. I'd probably say you couldn't return until the spirit left or you dismissed, it, however.

hmmm.... good question.

i say why not? it's possible for your body to get possessed while you're projecting, is it not? so why wouldn't it be possible for you to astrally project while posessed?

certainly there's no balance reason to disallow it that i can think of.

Well answer this - would you allow astral projection while a hostile spirit is possessing you? The answer needs to be the same for both, as your mind/spirit should be equally helpless (or not) in either situation.

i probably would, since you bring it up.

Would you allow a mystic adept to banish a possessing spirit?

well, depending on how you meant that, yes or no.

if you mean as a general rule, absolutely. banishing has no limitation on types, you banish all spirits equally.

if you mean, would i allow a currently possessed mystic adept to banish a possessing spirit (and in particular, implied, the spirit that is possessing them), then no. unless of course they somehow manage to astrally project, and do it from outside their body.

though the more i think about it, the more i'm not sure i would allow someone to astrally project while possessed (though absolutely, if they project before being possessed, i would allow that).

anyways, certainly if a mystic adept were to enter the astral (there's only one way for them to do so, as well... and it can be used on unwilling targets, so it's entirely possible for someone to project using that method, provided the astral gateway is being used to bring them onto the astral.

I'd allow the magician to pit his magic + willpower against the spirit's Force + Willpower before projecting.