Cannot communicate between two VM on the same physical machine using NAT IP Addressing

I have one physical machine, on it there are 2 virtual machines. One of the VM is the application machine, another is the db machine. All are running Windows XP.

I am using Sun Virtual Box for virtualization purpose.

One thing I notice is that on both virtual machines, the IP address is exactly the same.

The problem with this is that I can't connect to the db machine, using MySQL Administrator from my application machine, because I will have to specify the IP of server host, which, in this case, is exactly the same for both db machine and application machine!

I also try to use Hamachi address ( because the Hamachi address is different for different VM), but I always get a "cannot connect" problem, even though I can, from one VM, ping the Hamachi address of another VM.

Any idea how to solve this?

Edit: Dave has a correct answer. Here is the instruction on how to configure Sun Virtual Box 2.2 bridged connection.