I believe you cannot run the 'chown' command on a windows partition, since POSIX permissions/ownership are not supported by the filesystem.
The way I do it is to mount is with the uid= & gid= option.
/dev/hda1 /mnt/windows vfat defaults,uid=1000 0 0
or you could do
/dev/hda1 /mnt/windows vfat defaults,gid=100 0 0
That would mount it so users in group 100 could use it - it's up to you.