Unable to configure VM

Hi,

I asked this as part of another thread but it got lost once my main question was answered:

I've tried to reconfigure my Windows XP Pro VM but there doesn't seem to be any way to do it via the user interface (that is to say, I can edit the .pvs file to make some changes). If click on "VM Configuration", then try to edit any of the options, it says "Virtual machine configuration cannot be changed while virtual machine is running." If I try to stop the VM, the configuration screen goes bye-bye. Am I doing something wrong?

Pertinent details: Parallels Build 3124 running on MacBook (2.166 MHz/2 GB/16 GB) under OS X 10.4.10. Windows XP Pro installed via Transporter from my old Windows machine. It's set up with 512 MB of RAM and an 80 GB drive.

Thanks in advance,

Mark