If you decide to install Ubuntu (11.04) on your system, it will work with windows, however if you decide hat you no longer want it, and try to delete, you will lose ALL information on that drive, windows will not be able to format or Partition it.
The only way to recover the Harddrive is to use a low Level format program from the Harddrive manufacturers.
USB drives (including USB thumb drives) cannot be recovered this way as all the information required to format the disk is lost.
If you must try Ubuntu, run it from a CD or DVD on;ly.
It depends upon how you install Ubuntu; whether it was a dual boot system, whether it was installed on a separate partition or drive, in fact on a whole lot of variables.
What is true, is Windows is incapable of reading native Linux file systems, but, there's nothing to stop you installing Linux on a FAT file system if you want to. You just have to accept a serious performance hit. Furthermore, you can't blame Ubuntu for Windows substandard performance. Any decent partitioning software will format the drive. Partition Magic and GParted to name but two.
Not sure what you mean by that comment. Windows uses its own boot loader with which ever Windows OS . It does not need to allow for other OSs. If someone needs to dual boot or whatever then careful research should be used for both OSs.
I use various versions of linux on computers which also have Windows. I often remove or replace Linux and have never encountered the problem you describe. Please provide full details of what you have done and seen to help others understand exactly what has happened.