I want to mount windows 2003 oracle instance

I want to mount windows 2003 oracle instance to solaris machine. Can any one has idea? Please send me your experiences ,if any.

What do you mean by "mount windows 2003 oracle instance to solaris machine"?
Do you want to migrate an Oracle database from windows 2003 operating system to solaris or do you just want to query the database?

Using windows 2003 oracle instance for application installed in solaris.I want to query the database from solaris application.

You'll have to install an Oracle client on your solaris box. You can download it here.

What should I do next?

That installation will provide you with the executeable sqlplus. You can use that to query the database after some configuration (described in the installation-documentation).