Q:

Installing Ubuntu so that it can be removed without trace

I would like install Ubuntu on a laptop in a way that if I was to remove it, there would be no trace that I had installed it. I would dual boot it with Windows 7. Please could someone provide details of how I would go about removing it.

A:

I think the other 2 answers are incorrect. Because when you install Ubuntu, a bootloader called GRUB (offers which OS to boot) is written to the MBR of your hard-drive. And even if you wipe the ubuntu partition, GRUB will remain as a clear sign of that you installed another OS!

best option:  Using usb-flash-drive-boot (almost as fast as from hard-drive, silent, help here: http://www.ubuntu.com/download/help/create-a-usb-stick-on-windows) or a liveCD (slow and noisy).
2nd best option:  Backup the whole hard drive as it is, or at least the 2 system partitions of windows 7 (windows 7 has a 100MB reserved partition hidden from you), and restore it bit-by-bit. But for that you need an external storage drive possibly as large as the one in your laptop. (you can ask another question about the details of this)
bad option: The answer you actually seek is very complicated, error-prone, and I am not sure I could do it right the 1st time, and I AM POSSIBLY WRONG ABOUT THIS, so I do not recommend such, but here it is:

if you do not already have a 3rd partition available for ubuntu, than you must shrink the one windows 7 is on
back up the MasterBootRecord (MBR) of your hard-drive
install ubuntu on that new partition, which installs a boot-loader (called GRUB) onto the MBR (thats why backup is needed)
use it
recovery1: delete ubuntu partition from windows7
recovery2: re-grow the windows7 partition to "eat-up" ubuntu's (if you did step-1)
recovery3: restore the MBR (dangerous, expert needed)

