Virtualization of Windows on Ubuntu 11.10 64 bit
Solution 1:
At least for the time being, Virtualbox is the best solution to virtualize Windows desktops. It has support for 3D and 2D acceleration which improves the user experience. It also has easy support for USB. I also think the configuration GUI is a little bit more user friendly than virt-manager, though that's a nice GUI as well.
I've been told that we'll get SPICE in 12.04, and that may change things, but for now, go with Virtualbox.
Solution 2:
this question will open a debate about what is better than other but anyway.....
The answer for your first question is well explain in server fault section
well in my opinion VirtualBox is the guy for you.....
KVM
well kvm is more complex....KVM (for Kernel-based Virtual Machine) is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V). It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko. KVM also requires a modified QEMU although work is underway to get the required changes upstream.
Using KVM, one can run multiple virtual machines running unmodified Linux or Windows images. Each virtual machine has private virtualized hardware: a network card, disk, graphics adapter, etc.
The kernel component of KVM is included in mainline Linux, as of 2.6.20.
KVM is open source software.
Pre-installation checklist
Check that your CPU supports hardware virtualization
To run KVM, you need a processor that supports hardware virtualization. Intel and AMD both have developed extensions for their processors, deemed respectively Intel VT-x (code name Vanderpool) and AMD-V (code name Pacifica). To see if your processor supports one of these, you can review the output from this command:
egrep '(vmx|svm)' /proc/cpuinfo
or
egrep -c '(vmx|svm)' /proc/cpuinfo
If 0 it means that your CPU doesn't support hardware virtualization.
If 1 (or more) it does - but you still need to make sure that virtualization is enabled in the BIOS.
Yes KVM have a GUI :
apt-get install virt-manager