OS X runs via an emulation program, yes. No one's dual booting XP and OS X--at least, not that I know of. If they've progressed beyond an emulated install to full usage, please link me to some screenshots and "how we did this" pages. I'd love to be proven wrong on this.
There are a list of install techniques discussed here...
http://wiki.osx86project.org/wiki/index.php/Installation_Guides
Most of them are native, with only a couple using VMware.
It still sounds like something of a black art, but it is certainly a popular geek pastime.
The Mac OS X operating system will run in native execution mode (i.e., full speed) on Intel hardware. The emulation mode is used only when executing PowerPC-native application code on Intel hardware.
No one's dual booting XP and OS X--at least, not that I know of. If they've progressed beyond an emulated install to full usage, please link me to some screenshots and "how we did this" pages. I'd love to be proven wrong on this.
I believe dual-boot XP and OS X has been working for a while on the ADP hardware, and there are reports of several hacked versions of Mac OS X for various PC brands.