how can I configure the bittorrent downloader?

You can goto System --> preferences --> Main Menu, and add the icon for bittorrent back to the menu.

well

that gets me to a "select .torrent file" dialog.

what I mean is that I want to graphically configure bittorrent parameters like "listen ports", etc.

I forgot to tell

I tried with btdownload-gui, but I keeps on giving an error (I found a pair of bug reports about it, but they didn't solve anything in my case)

You might want to try a more full featured torrent client like ktorrent, you can install this in a terminal by using 'sudo apt-get install ktorrent' or, using Add/Remove programs in Gnome.

yeah

I use utorrent (and sometimes, azureus).

but I'd like to know how to configure gnome-bt, just 'cause it comes in Ubuntu by default and surely there'll be some friends asking me for it (also, I'm stubborn with this kind of things)

Understandable, though a forewarning the configuration directives are very basic. There are 2 different configuration files, you can edit these in gnome by hitting <alt>+<f2> to open the run command dialog.
File #1
'gedit ~/.gconf/apps/gnome-btdownload/%gconf.xml'
<?xml version="1.0"?>
<gconf>
        <entry name="previous_path" mtime="1179278065" type="string">
                <stringvalue>/home/david/torrents</stringvalue><--THIS IS THE DIRECTORY YOU WANT TO SAVE TORRENTS IN
        </entry>
</gconf>
File #2
'gedit ~/.gconf/apps/gnome-btdownload/settings/%gconf.xml'
<?xml version="1.0"?>
<gconf>
        <entry name="cap_upload_peers" mtime="1179281631" type="int" value="5"> <--5 =HOW MANY PEERS
        </entry>
        <entry name="cap_upload_rate" mtime="1179281626" type="bool" value="true"> <--true = TO CAP or UNCAP UPLOADS
        </entry>
        <entry name="cap_upload" mtime="1179281625" type="bool" value="true"> <--true =SET SAME AS ABOVE
        </entry>
        <entry name="cap_upload_rate_kbps" mtime="1179281635" type="float" value="8"> <--8 = Kbps TO LIMIT UPLOAD RATE
        </entry>
</gconf>

I hope this helps, gnome-bt frontend just really is not meant to be configured like a more featured torrent client.

If this answered your question, could you please mark it solved?
Thanks,
David P.

well

it's not like I'm completelly answered, but there's no point on going on with this.

I think by "that config-gui" you mean gconf-editor. Run gconf-editor and find the configuration under /apps/gnome-btdownload.