If you mean "how do I resize the screen in OS X" then the answer is:
1. Open the System Preferences (either from the Dock or from the Apple menu). (It looks like a light switch)
2. Open the Displays Panel and choose the Display tab.
3. On the left of the Displays tab you can select one of the Resolutions from the list.
4. Quit or close the System Preferences when done.
Remember, when using an OS in a VM, think of it as a real computer, because that is essentially what it is. So, to make changes to a Mac, think like a Mac user! 
Most likely yes. I have not used OS X in a VM in some time, (I was given an iMac as a gift! 
)
IIRC, Mac OS will only report the screen resolutions it believes are viable for the hardware. There is likely a way to change it through the shell, although, I don't know if this is a good idea... Make certain to take a snapshot of the OS if you plan on trying this.
By using a tool like this:
http://lists.apple.com/archives/macos-x-server/2004/Sep/msg00948.html
Note, if you are not familiar with using a Unix command line (bash) I suggest you don't do this. But if you want to give it a shot make certain you take a snapshot of the OS first!
If I remember correctly, OS X is not supported in a VM, so a whole bunch of things that would normally work in it do not work in a VM. In all honesty, you are probably better off leaving it at the resolution you have it at. Yeah, I know that sucks. Sorry.