Facing a very strange problem

When I insert the Oracle 9i CD-1 to install the Oracle on Win2000 server and when choose install option, after few seconds a message appears on screen i.e.
"Error writing to directory c:\pathname, please ensure that this directory is writable and have atleast 25 MB free space. Installation can not continue"

Kindly note the there is space avaiable on harddisk in GB's and it is writable. Then why this error is coming.?

Confused !!!!