Are you running this webserver? or is it being hosted.
You can use the chown() command, but I believe it the user has to be a superuser to run it.
I had the same prob with my hosting space...
FTP user is different than the apache user.
Basically you have to change what user apache runs as....
You could use php ftp commands and hard code the username/pwd for your ftp..........
If you are paying for webspace, it's unlikely you will be able to solve this problem..