The easiest way to get Postgis up and running on (K)Ubuntu 10.10 is to use the PPA.
Here the instructions
Add the PPA to your Software Sources Run Kpackagekit (or Synaptic), go to sources and add an additional source by pasting this
Refresh your sources and then search for postgis and install the package “postgresql-8.4-postgis”
or by command line sudo aptitude install postgresql-8.4-postgis
another gotcha If you want to connect to postgis with a custom user and get this error message psql: FATAL: Ident authentication failed for user “username”
edit /etc/postgresql/8.4/main/pg_hba.conf and comment out line below and add the line below.
# Database administrative login by UNIX sockets #local all all ident local all all md5