# Transmission v2.51 is currently recommanded to run the RPC (daemon) version.
# in fact, you need a version >= 2.40, because some RPC constants were modified.

# check the latest versions here :
# http://mirror.pnl.gov/ubuntu//pool/main/t/transmission/

# sample for a manual installation on x86 :

wget http://mirror.pnl.gov/ubuntu//pool/main/t/transmission/transmission-cli_2.51-0ubuntu1_i386.deb
wget http://mirror.pnl.gov/ubuntu//pool/main/t/transmission/transmission-common_2.51-0ubuntu1.1_all.deb
wget http://mirror.pnl.gov/ubuntu//pool/main/t/transmission/transmission-daemon_2.51-0ubuntu1.1_i386.deb

dpkg -i transmission-common_2.51-0ubuntu1.1_all.deb transmission-daemon_2.51-0ubuntu1.1_i386.deb transmission-cli_2.51-0ubuntu1_i386.deb

Note:
To install the 2.61 (tested ok too), a newer libnatpmp1 is required :
 http://mirror.pnl.gov/ubuntu//pool/main/libn/libnatpmp/libnatpmp1_20110808-3ubuntu2_i386.deb