Any way to run Linux as a Virtual Machine on top of Windows so can have best of both worlds?

Lots of options here:

Tools Only

If you just want the GNU/Linux tools, there are a few choices.

• cygwin gives you a bash shell with lots of tools, including an X11 server. This has been around awhile and is mature.
• msys is a smaller, lightweight alternative to cygwin.
• GNU utilities for Win32 is another lightweight alternative. These are native versions of the tools, as opposed to cygwin which requires a cygwin DLL to fake out its tools into thinking they are running on Linux.
• UWIN is a set of Unix tools/libraries from ATT Research that run on Windows.
• SUA is Microsoft's Subsystem for UNIX-based Applications, offering a tools and an environment for building/running Unix programs under Windows.

Linux in a Windows Process

There are several packages that will run Linux as a Windows process, without simulating an entire PC as virtualization does. They use Cooperative Linux, a.k.a. coLinux, which is limited to 32-bit systems. These don't have the overhead of virtualizing, and they start up faster since you're not booting a virtual PC. This is a little more on the experimental side and may not be as stable as some of the virtualization options.

• Portable Ubuntu
• andLinux

Virtualization

Virtualization software lets you boot up another OS in a virtual PC, one that shares hardware with the host OS. This is pretty tried-and-true. There are nice options here for taking snapshots of your Virtual PC in a particular state, suspend/resume a virtual PC, etc. It's nice to be able to experiment with a virtual PC, add a few packages, then revert to a previous snapshot and "start clean".

• VMWare
• VirtualBox
• VirtualPC

Dual Booting

• wubi allows you to install Ubuntu right from Windows, then dual-boot. Not as convenient as the above, since you can't run both OS's at once.

It looks like VirtualBox runs on Windows, which should have decent Linux support. Virtual PC, as far as I know, does not offer very good Linux integration.

If you're just looking for the regular set of command line tools, you might look at cygwin. A lot of the goodness without the overhead of maintaining a separate system.

An alternative to a virtual machine (meaning it can share RAM with Windows) is Portable Ubuntu, which runs Ubuntu as a Windows app. It's one of the niftiest ways to get the best of both. I can't post a link because I'm a new user here. The domain is: portableubuntu.demonccc.cloudius.com.ar

Maybe andLinux would be interesting?

From andlinux.org:

andLinux is a complete Ubuntu Linux system running seamlessly in Windows 2000 based systems (2000, XP, 2003, Vista, 7; 32-bit versions only).

You can use cygwin if you just want the tools.

You can use VirtualPC software to mount any Linux.

There are a few distros that install on top of Windows like phat linux

Many useful linux utils (including bash) have been ported to native win32 (unix utils).

It's not the job of the Ubuntu CD-ROM to provide virtualised installation.

Just install VirtualBox, and then create a new virtual machine booted from the Ubuntu disc.

Alternatively get VMWare Player and download a pre-made image.

You can run it in a virtual machine ala VMWare, but there's also Wubi, which you might find suitable.

VMWare gave me Ubuntu for a while, but then I used VMWare to create a virtual machine of Windows, then I installed Ubuntu and Windows in Ubuntu.

In terms of UNIX tools there is of course the Microsoft Unix for Windows.

ATT Research also provides UWIN.

"Cooperative Linux (short-named coLinux) is a port of the Linux kernel that allows it to run cooperatively alongside another operating system on a single machine."

http://www.colinux.org/