I don't know of a way to boot into a VM that is already running through PXE. Reading your post it actually doesn't sound like what you really want to do anyways. None the less here are two possible ways that will work for you.
The first and probably the easiest is to install a lightweight Linux OS on your P4 machine. From there set it up to remote desktop into the openSUSE VM running on your main PC. You could set up a task to automatically make it connect to the openSUSE VM as soon as the lightweight OS loads. You wouldn't need a hard drive to install the lightweight OS on, it could run off of a USB stick or compact flash card. The openSUSE VM will still be running on your main PC and using its resources.
The second option and more complicated would be to set up a PXE boot system. Your going to need to set this up differently though. You'll start with making another VM of linux (debian based preferably for the packages I'm mentioning). This will then need a program like FOG or DRBL installed. FOG or DRBL will handle the PXE boot process and image capture and loading. It will be the server for all of your installations. You can setup custom images that you can then PXE boot from any machine with a capable NIC.
From there you can use either one of those programs to convert your existing openSUSE VM you have now to the proper format to be able to PXE boot it. You can also setup VMware to PXE boot the openSUSE image as well after your have converted it.
Here is the issue though with PXE booting that you may not be fully aware of. You can boot an image of a system over the network but changes to that image will not be saved, so any changes you make will be not be there the next time your boot the image. If you want the image to be dynamic you will have to capture the image before you shut down every time. Unless your network and drives are really fast this can take a bit of time and is usually more headache than it is worth.
If you just want to use your existing VM on the P4 machine then I'd really recommend booting a lightweight OS and then remoting into the openSUSE VM. This will keep the VM running on your main PC and it will use all of its resources. If you PXE boot then the OS will use the P4's resources and could be much slower (if your P4 isn't 64-bit capable then you'll have to switch to a 32-bit as well).
I was running a FOG system myself to boot an XBMC image over my network to HTPCs so I can point you in the right direction with it if that is the route you want to take. There are some pretty good tutorials on the websites as well.