Are virtual machines running in OSX sandboxed? ie. If I am running a Windows virtual machine and I get corrupted with viruses and worms, will it affect OSX in any way shape or form?
It depends on your settings - it can be sandboxed (which is the way I personally like it) or you can make it easier to go back and forth. The default settings should be safe, but you can disable HGFS shared folders, uninstall Tools, turn off networking, and so on.
Are virtual machines running in OSX sandboxed? ie. If I am running a Windows virtual machine and I get corrupted with viruses and worms, will it affect OSX in any way shape or form?
If you take the default settings on a Windows Easy Install and have installed VMware Tools then the Host has potential to be vulnerable however you can do as Eric suggested things like disable sharing, disconnect the network and uninstall VMware Tools.