Upload images

I have installed WordPress on my domain.

It all seems to work okay apart from when I try and upload an image on a post. I get an error ‘ The uploaded file could not be moved to’ in the upload box.

I guess this is something to do with permissions and have read the support note at:
http://codex.wordpress.org/Changing_File_Permissions

However I can’t change the permissions via my ftp account or via its Plesk Control Panel – the host doesn’t allow it.

Any help would be appreciated.

Thanks