Create image of Windows partition on Linux
ntfsclone is awesome. I've used it with great success to clone systems and for backup purposes.
If your Windows partition is not using NTFS, dd should take care of you -- although it's not terribly efficient.
dd would seem to be the go to choice here. The command would look like the following...replace the device and output file with whatever you wish.
dd if=/dev/sda1 of=~/windows.img
There is also partimage and ghost4linux. But for something like this both of those may be overkill and overcomplicating things.