In general you don't need to remove Grub from your system. You can just comment out the Ubuntu installation boot partition from the menu, and leave the Vista line alone.
If you wish to remove Grub you typically would need the installation disk or any Windows CD for the fixmbr program to replace the Grub loader, but I would recommend just leaving it alone and doing the commenting out from the above paragraph.
You have to install both operating systems to get a 'dual boot' system. I would suggest installing vista first, then installing ubuntu. Doing it the other way around will mean that the ubuntu installation will not be recognized after you install Vista, so do the Vista install first.The Ubuntu Grub loader will be able to recognize the Vista partition and should present you with a menu when you boot the machine as to which operating system you want to use.The easiest approach to this would be to install Vista on one partition and ubuntu on a different partition of your hard drive.
You can remove the partition safely using a tool such as a gparted live cd. You need to burn the image to a CD-rom, boot from that, and remove the partition Ubuntu is installed to. Note: If you installed GRUB to the Master Boot Record of your hard disk, removing the Ubuntu partition could cause booting complications. These should be fixed upon reinstallation of Ubuntu.
Yes, if you have copied all installion files on your hard disk. If you haven't you cannot reinstall Vista.
There are many ways, but the easiest is to use a Windows 7 installation disk to delete the partition.
Wubi can only be used to install Ubuntu. (It stands for Windows-based Ubuntu Installer).
Yes, you can. But you will have repartion and reformat the hard drive.
This varies from installation to installation. My particular installation takes up about 6.7 GB of memory.
Yes by buying a window vista installation CD.
Any version of Windows and Ubuntu is no problem. I'm unaware of all the issues that might surround a Windows 7 / Vista dual-boot, but adding Ubuntu into the mix shouldn't cause any problems, provided the two versions of Windows are cooperating.
Ubuntu, as any operating system, has certain requirements for it's users with respect to hardware. You may check the required features by clicking on the link below.If your computer can run Ubuntu, you should be able to download and install Ubuntu as a dual boot on the system without deleting Vista. (Note: I highly recommend backing up your hard drive before dual booting anything.)You may see the method of doing that by clicking on the link below.
Install Vista first. During the installation of OpenSUSE, you will be prompted if you would like to partition the hard drive to make room for OpenSUSE, or format the drive entirely for OpenSUSE. Make a partition of at least 6 GB, plus a swap partition of 1 GB. The installer will automatically install a bootloader known as GRUB, which can boot Vista or OpenSUSE at your choosing.
It depends on what edition you have and what you enable, but my Vista installation (Vista Home Premium) took 10GB of space.