Since people still seem to be having trouble with this, and since some instructions given so far seem kind of bogus (one link's installation instructions are "download this"), I thought I'd try to help...
Assuming your problem isn't getting wxPython compiled on Gentoo (my answer for that is don't use Gentoo
(If you're just having problems getting torrents to launch from a browser, skip to the end and try that first.)
0. If you're using packages, just reinstalling them may take care of everything.
0.5. If you're copying files manually, just remember to copy the BitTornado directory too; it needs to be in the same directory as the bt*.py files, or in one of the python lib directories. (This bit seems to be missing from some suggestions. If this fixes things, great, you're done.)
1. It's possible that different bittorent clients and leftover files are conflicting with eachother. Uninstall any bittorrent / bittornado / etc packages, and delete any remaining bittorrent related files (bt*.py) and directories (BitTornado, Bittorent) from anywhere in your path and anywhere Python looks for them. If you don't know where those are, look in /usr/bin, /usr/local/bin, /usr/lib/python2.x and /usr/lib/python2.x/site-packages, and python2.x and python2.x/site-packages in /usr/local/lib. (Don't delete everything in /usr/lib/python2.x. That would be bad. Well, you'd just have to reinstall python and most things that use it. Also /usr/bin. That would be VERY bad.)
2. Download and untar bittornado.
3. If you don't care about launching torrents directly from a browser, the easiest way to run bittornado is to go to the directory and run it from there. Regardless, read docs/INSTALL.unix.txt, it has directions for getting torrents to launch from a web browser. It also gives the easy directions for installing, run: python setup.py install
(After running the setup script, the directory can be deleted.)
(It's probably best to just run the setup script than copying files manually - see 0.5.)
For completeness, and for the lazy, the contents of INSTALL.unix.txt:
install Python, version 2.0 or later - http://python.org/
install wxPython - http://wxpython.org/
(under debian, you can currently get the above using
apt-get install libwxgtk2.2-python
from testing and use python 2.1)
untar and run: python setup.py install
put a line in /etc/mailcap which is similar to the
following, only replace the path to
/usr/bin/btdownloadgui.py with the one it's actually in.
application/x-bittorrent; /usr/bin/btdownloadgui.py %s; test=test -n "$DISPLAY"
You may have to restart your web browser for it to start
If you're using a web browser which doesn't respect
/etc/mailcap you can go into the mimetype configuration for
your web browser and manually associate application/x-bittorrent
with btdownloadgui.py (with the appropriate path, of course.)
Hope this helps.