Ubuntu is a great operating system and very few people want to uninstall it after they get it, however, sometimes it is necessary. For example, I had the need to take Ubuntu off of my laptop after I installed it and couldn't get my wireless card working. Instead of completely reformatting your computer, use the following steps to remove it and recover that space without data loss.

Please note that this guide is for a Windows-Ubuntu dual-boot situation. If you are doing a triple-boot don't use this guide.

Step 1 - Get rid of GRUB
Take a Windows boot CD (I even used my XP CD to do this on my Vista install, so don't worry about version differences). Boot to it and choose the recovery console. Within the recovery console, type the command fixmbr and press enter. It will most likely warn you that you have a non-standard or corrupt boot record and that running fixmbr could render your computer unbootable. Tell it to run by typing y and pressing enter. GRUB is now gone, and your computer will run Windows immediately on boot instead of offering a boot menu.

Step 2 - Re-Allocate that space that Ubuntu used
Put in your Ubuntu LiveCD and boot to it. Go to System -> Administration -> Partition Editor (this application is also known as Gparted). When it loads, select your Ubuntu partition (it will most likely be formatted ext3), right click, and select Delete. Then, select your Windows partition (will be formatted NTFS and flagged "boot"), right click and select "Expand" (I believe that is what it is called). At the top, slide the slider to the size you want the partition to be. Click OK. To apply these changes, click the Apply button (the green checkmark) at the top of the Window. The process of expanding your Windows partition will take a very long time, expanding my 40GB Windows partition back to 180GB took about 1 1/2 hours. You will still be losing about 5GB to the Linux swap partition, you could try unmounting it before running Partition Editor, it should then be able to remove it (I have not personally tried this, but it should work).

Really, it isn't that hard, just time consuming. Hope someone found this guide useful.