Well I have it now. But it did not replace the 1.6.3 version. It does need to run with some parameters otherwise I get an error.
mike@ubuntu:~/Mongo181/mongodb-linux-x86_64-1.8.1/bin$ mongod
/usr/lib/mongodb/mongod --help for help and startup options
Sat May 14 07:21:00 MongoDB starting : pid=11956 port=27017 dbpath=/data/db/ 64-bit
Sat May 14 07:21:00 db version v1.6.3, pdfile version 4.5
Sat May 14 07:21:00 git version: nogitversion
Sat May 14 07:21:00 sys info: Linux allspice 2.6.24-28-server #1 SMP Wed Aug 18 21:17:51 UTC 2010 x86_64 BOOST_LIB_VERSION=1_42
Sat May 14 07:21:00 exception in initAndListen std::exception: dbpath (/data/db/) does not exist, terminating
Sat May 14 07:21:00 dbexit:
Sat May 14 07:21:00 shutdown: going to close listening sockets...
Sat May 14 07:21:00 shutdown: going to flush oplog...
Sat May 14 07:21:00 shutdown: going to close sockets...
Sat May 14 07:21:00 shutdown: waiting for fs preallocator...
Sat May 14 07:21:00 shutdown: closing all files...
Sat May 14 07:21:00 closeAllFiles() finished
Sat May 14 07:21:00 dbexit: really exiting now
It still looks like the old version :((