Windows XP is installed in my C drive. Can I install an another fresh copy of Windows XP or Linux or Windows 7 in same C drive without formatting the previous one?
Absolutely, the only times there are problems are sometimes when you try to install an older OS second as they usually build in backward compatibility to the newer OSs, whilst the older ones can remove features needed for the newer OS (e.g. Windows XP overwrites the Windows Vista / Windows 7 boot loader, whilst this newer boot loader is compatible with XP).
Just install in a good order and it should work fine. If you get any specific problems, feel free to ask here!
Just remember, if using Windows, select a different folder as they can't co-exist in
However, to stop compatibility issues, it is always best to use different drives (or even virtualisation).
You can install multiple operating systems on one drive. That's one of the main reasons for partitions.
Your “c: drive” is in fact not the whole disk: it's a partition. That partition probably uses all the space on the disk, minus the first sector which contains the partition table (and a few other things).
To install another operating system, you'll need to make space for it. Most Linux distributions will handle this as part of the installation process, giving you an option to shrink the existing Windows partition. I don't know if that feature is available in the Windows installer.
You can make several Windows versions cohabit on the same partition (at least with some combinations of versions). They'll use different system directories (e.g.
c:\\win7). They'll share other elements such as
Program Files (unless you go out of your way, and perhaps even if you do), which might be a problem if you have software that's incompatible with one of the versions.
Ubuntu offers a way to install Linux in a file on a Windows partition: Wubi. It's tempting if you're a Windows user who wants to try out Linux, but it'll make your Linux installation dependent on Windows, which is not good for reliability (messing up in Windows could destroy your Linux installation).
You need at least an other partition on that drive. Especially true if you want to install win7 because it requires a different formating.