Virtualization on top of virtualization

I wanted to have both VMWare Workstation 6 and Microsoft Virtual PC 2007 (both are free and in beta) at the same time on my XP Pro machine. I was concerned that they would conflict. Actually, I found no info on the Web if there is a conflict or not. So I decided to install VMWare and VPC on SVS. This way, I can keep the two programs separated by "turn on" one or the other when I need to use it. Unfortunately, the virtual NICs in VMWare did not installed at all on top of SVS and VPC works initially, but when I restart the XP host and then relaunch VPC, there is an error about some driver and VPC would not launch. In short, I cannot install either VMWare and VPC on top of SVS. I will push ahead and install both VMWare and VPC without SVS and see if they do conflict.