I have both Windows and Linux partitions on my system. I wanted to be able to run Linux via VMWare. To accomplish this, I created a VMWare instance using the raw disk support feature.

Then, I booted the Ubuntu Live CD from within this instance and determined what device the Linux / partition is on my hard disk (it's /dev/hda4).

Next, I added the following to the end of /boot/grub/menu.lst:

title		Ubuntu, kernel 2.6.15-23-386 (VMWare)
root		(hd0,3)
kernel		/boot/vmlinuz-2.6.15-23-386 root=/dev/hda4 ro quiet splash
initrd		/boot/initrd.img-2.6.15-23-386
savedefault
boot

I only have 2 Linux partitions, / as ext3, and a swap partition. I don't know if this trick would work if I had more than 2 partitions. I'd probably have to change /etc/fstab before booting inside VMWare.

The next step is to install VMWare tools inside Linux, so I can cut and paste between the OSs.

When I'm not running VMWare, I use EXT2 IFS for Windows to access my Linux partition.

Using these tricks, I'm never too far away from my preferred OS.

I've yet to try running my Windows partition virtually from within Linux, as I'm sure that Windows will want me to reactivate, when it sees the hardware changing. Even if that wasn't the case, Windows may crash when it sees a different environment. Who knows?!