yes
zerowii
Yes
Yes. DeSmuME is available for Mac OS X.
There is a Dreamcast emulator, known as lxdream, under active development for Linux and Mac OS X. It is not completely stable yet and is only capable of running a few games.
Dolphin runs on Mac OS X, though I don't think there are currently any official packages available, so you have to compile it yourself.
No. You can also get it for Xbox 360, PS3, Wii, iPod Touch, Nintendo DS, Mac OS X, and Microsoft Windows.
Classic Mac OS games can be used in Mac OS X if the Mac is a PowerPC Mac, the game was written for PowerPC processors, and the version of Mac OS X is Tiger or older. They cannot be used on Intel Macs except via the use of a third-party emulator, such as SheepShaver.
Microsoft Windows/Mac OS X, Nintendo DS, Nintendo GameCube, Nokia N-Gage, PlayStation 2, PlayStation 3, PlayStation Portable, Wii, Xbox, Xbox 360, iOS, Blackberry
No, for all of the Old World macs (pretty much MacOS 2.0 -9.2 ) you need the ROM image. The system needs the information on the ROM chip to run.
I am afraid that the .n64save and .n64freeze formats are used only by the propriety n64 emulator for Mac OS X, Sixtytforce. [www.sixtyforce.com]
DOSBox is cross-platform. It runs on Windows, Linux, Mac OS X, BeOS, FreeBSD, NetBSD, OpenBSD, OS/2, Palm OS, Sony PSP, Nintendo Wii, and GP32x. It is designed to be easily portable, and thus can probably be run on other besides these.
PowerPC Mac OS X apps are emulated transparently on Intel Macs. For "Classic" programs, you'll have to use an emulator like SheepShaver.
VirtualPC can do that. There is a port of QEMU to Mac OS X that should run even better, but it is a bit more difficult to use.
No, bootcamp is not required for virtual machines which are running from mac os x. Parallels is a virtual machine emulator you can put any virtual OS into it without disturbing your Mac OS X system setup. Bootcamp is used when you are installing windows natively on the mac.