Hi I tried out Ubuntu but wasn't happy, so I tried to restore windows from my laptop's CD, but after the restoration process finishes and the system reboots I get "GRUB loading, Error 17".
How can I fix this?
Sounds like the restore didn't wipe out the Grub (Ubuntu) bootloader. If you have a Windows installer disk (either CD or bootable USB), you should boot it up and use it to re-install the Windows bootloader. Boot into the CD, and select the Startup Repair option (I believe it's in the System Recovery Options menu item). After it's done, you should be able to boot into Windows without any problem.
The problem is that the windows and linux bootloaders (the little menu that lets you chose an OS to boot into) don't play well together. Well, specifically, the windows boot loader doesn't play well with grub, grub plays with everyone.
So, if you boot back into a live session and reinstall the linux bootloader (grub2) yiou should be able to boot into windows. Once there, you can clear the MBR and you should be fine.
For a howto on reinstalling grub2 from the Ubuntu live disk, look at point 13 on this page. At this point, you should at least have a working system. For help on reinstalling the windows bootloader, look here.