The short version:
$ nautilus sftp://test.com
brings up a file-browser window with test.com in it, which I can then browse and click around in. Also, test.com is mounted as ~/.gvfs/sftp on test.com/
Yes, it has all those blanks. Oh well. You can still get to it on the command line and in scripts.
If you already have a file-browser window up, just use the URI sftp://test.com
If you need to go in through a different port from 22, say 666, you'll first need to add a pair of lines to your .ssh/config file that look like like this:
Host test.comPort 666
You can test whether they work or not by using ssh by hand.
$ ssh test.com