there should be a option within windows to create recovery media. I used a flash drive for my windows 8 machine. this comes straight from microsofts website how to create recovery media.
Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search.)
Enter recovery drive in the search box, and then tap or click Create a recovery drive.
Administrator permission required You might be asked for an admin password or to confirm your choice.
After the recovery drive tool opens, make sure the Copy the recovery partition from the PC to the recovery drive check box is selected, and then tap or click Next.
If your PC doesn’t have a recovery partition, then the checkbox is greyed out and the recovery drive will include only the recovery tools and a bootable image, but not a recovery image to use for refreshing or resetting your PC.
Insert a USB flash drive into your PC that is at least as large as the size indicated on the screen.
Tap or click the USB drive you would like to use for your recovery drive, then tap or click Next.
Tap or click Create.
The recovery image and necessary recovery tools will be copied to your USB flash drive, which will take a while, depending on your PC and the size of the recovery image.
When the process is done, do one of the following:
If you want to keep the recovery partition on your PC, tap or click Finish.
If you want to remove the recovery partition from your PC and free up disk space, tap or click Delete the recovery partition. Then tap or click Delete. This will free up the disk space used to store your recovery image. When the removal is done, tap or click Finish.
Remove the USB flash drive.
This is now your Windows 8.1 recovery drive, and you'll need it if you ever need to refresh or reset your PC. Keep it in a safe place and don't use it to store other files or data.
If your PC came with Windows 8 and you upgraded it to Windows 8.1, your recovery drive will include Windows 8, and you’ll need to upgrade to Windows 8.1 after you refresh or reset your PC.
I have been using Ubuntu and sabayon in dual boot configuration, converted my disc to MBR, and completely wiped all traces of windows 8 off my system. Hopefully that helps you figure out what you need to do to backup windows. you could just install ubuntu alongside windows 8.1 as well. Ubuntus installer is very helpful in helping you figure out how much space you want to give to ubuntu.