I think this is the right forum

My band is thinking about buying a PA system, and i've heard about powered mixers. Should we get a package with a powered mixer or try to find one with a mixer and a power amp? Is either one better than the other? What's the difference?

When all else fails, ask the pit.
i, personally, would go for a mixer and power amp separately. it just gives you more options when you are looking for stuff. also, you can then use the mixer for recording to a computer or something by just not using the power amp. depending on how many mics you want, you can get a pretty good mixer for a couple hundred dollars. for example, some peavey mixers:
6 channel
10 channel
14 channel
then you can get a nice poweramp for a bit more than that. i dont know much about power amps really, but something like this or this seems to deliver a pretty fair ammount of power so you can get some nice headroom for your vocals.

i just kinda feel that separate units gives you more flexibility and allows more ease for upgrading down the line.