Generally to install Koha on Ubuntu Dapper Drake's amd64 platform you can just follow the instructions at http://www.kohadocs.org/Installing_Koha_on_Debian_sarge.html, but I found a few differences while I was going through it.
Note that I used the server edition rather than the desktop version.
Before installing “Event” from CPAN, install the build-essential package via apt-get. This will allow Event to install without failing.
Note that presently there are packages for the Yaz toolkit in Ubuntu universe, but they are a little old. If you're just doing a plain install of Koha without updating to cvs or using Zebra, they're probably fine, but if you're planning on using the Zebra plugin then you should download the Yaz source tarball instead, and compile the packages yourself. (This is because installing Net::Z3950::ZOOM will fail because the version of Yaz is too old.)
The folks at Index Data have already done the package configuration for Yaz (and Zebra) so creating packages from the source is fairly simple:
If you are planning on installing zebra, you can follow the same procedure (downloading the idzebra tarball from /pub/zebra, of course).