I'm new to both Linux and Drupal, but I can see that the owner and group assigned to the drupal modules directory is one of my SU accounts on the server. When I log on to SFTP I use that same credential.
I tried to upload a module using Aptana studio and it tells me it can't create folders.
Do you feel that there's additional ownership info needed on the server side? Would my folder rights not be applicable when connecting via SFTP?