With QEMU or Xen, there were problems I couldn't fix (this because my Linux is heavily customized and not running kernel from openSuSE anymore). I also tried the pre-compiled (proprietary/non-OSE) version, and this actually even better. As mentioned on the website, the proprietary version supports USB and file sharing between host and guest O/S.
So far, I am able to run my Windows XP Pro SP3 under this Linux 64-bit with no problem. I could print, browse internet and even play games (eventhough it is slower than running in native/standalon XP). With file sharing, I could install Microsoft Office in the guest O/S and share the doc/xls/ppt files.
For the networking, the VB provides a firewall and NAT. The subnet it gives is in 10.x.x.x subnet, but work with no issues.
I still have small issue though as the screen resolution under XP is limited to 1024x968, eventhough the host O/S (Linux) has nvidia driver and was running resolution 1680x1050. But interestingly, on my MacBook running OSX 10.4 Tiger, I could set the screen resolution as much as 1680x1050 (which is even beyond my laptop resolution). Why?
With Windows XP as host O/S, I initially tried Microsoft Virtual PC. The interface is good, but when I installed Linux OpenSUSE 10.3 (32-bit), the network worked sporadically and took almost a week to download necessary modules from opensuse.org! I tried installed offline, the same issue happened.
After this painful waiting, finally I managed to install it, but everytime I rebooted the guest O/S it never came up correctly (the screen stayed blank after the initial OpenSUSE login screen). I eventually dumped this stupid Virtualization tool completely and install VirtualBox. Yes, as you might guess, it works like a charm on Windows XP too.
I still need to try on Windows Vista though. Will report it later.
What a tool!