Hi,
Like Windows XP OS, when we will install a software it will go by default to C drive's Program file directory.
So similarly if we will install the software in the Linux OS, where it will go by default ?
Depends of the flavour...
But one thing that is true on all unix:
From unix point of vue there is no such thing as c:, d: e: etc...
The origin is root /
On XP, software is installed by default to whatever location is programmed into the installer (e.g. MSI or Installshield) by the software manufacturers -- this is not decided by the operating system. It is not so different on Unix, but there is the Filesystem Hierarchy Standard which describes where things ought to go in Linux.
In RPM based Linux, the software usually tends to install in /usr or /usr/local or even /opt.
RPM and DEB packages will automatically install the software in whatever directory they are supposed to go.
You can put tar balls anywhere you want, but be careful. It is always a good idea to put your 3rd party software in /opt. 
For more info read this.
-Nitin
If its RPM then install-root is /. This install-root can be changed with option "relocate". In case if you compiling from source then default prefix/exec-prefix is either /usr or /usr/local.