I mounted FAT32 file system on /win. I can easily write file onto that partion with root login. But when I try to write a file with a php script via web browser, I gives me error 'unable to write file...' When I change permissions with 'chmod 777 /win', it gives me error 'cannot change the permission from 755 to 777 (or something similar)'.Please tell me whats wrong...???

I don't exactly know, but seems like a FAT32 limitation.

Probably, what you have is a "mount point" (/win) where you "mounted" a FAT32 file-system (i.e. /dev/hda3)
What you are trying with chmod is to change the mount point permissions, but, is FAT32 able to assume a unix permission settings?

Try with a unix filesystem.

Also note that when you upload a file via web, you are not writing (hopefully) with root permissions, but with the web server user (probably "nobody")

Also, you have to check your directory permissions within the webserver config.

To change the permissions for a FAT32 partition, you will have to edit /etc/fstab and add a few options on the line for the FAT32 entry.
The uid options sets the owner.
The gid options sets the group.
The umask options sets the permissions.

Take a look at this post for some examples.
http://www.linuxquestions.org/questi...499#post454499

Also, read about the options in the mount command's MAN page.