Reset the password for a user when Snow Leopard is running as a VM?
A quick solution to the problem is to simply make a new admin account with a password you know. The details are covered step by step in another answer, but here is the summary:

You should be able to mount the disk image of the mac using vmware tools and delete the /private/var/db/.AppleSetupDone file. Upon the next boot of the VM, you will be prompted to create a new admin user whereby you can choose a new unique short name (to avoid stomping on an existing account) and use that admin account to reset the other user's password.

If you truly need to enter single user mode from inside your virtual machine, simply remap the keys as described in this KB article from VMWare:


Switching Mac OS to Single User Mode