Ubuntu 9.10 includes CouchDB in the standard desktop installation ... perhaps that's all you need?
Personally, I like to track CouchDB trunk but building on the latest Ubuntu is not quite as easy as it used to be. The following is mostly from memory so may not be quite right ...
The list of packages in the CouchDB README to compile from source does not work (at least, not for me). Instead, ensure your apt sources are up to date and install the following packages:
$ sudo apt-get install build-essential erlang-nox erlang-dev libicu-dev xulrunner-dev libcurl4-openssl-dev
Next, configure CouchDB to use xulrunner's headers and libraries, using a custom LD_RUN_PATH:
$ LD_RUN_PATH=/usr/lib/xulrunner-188.8.131.52 ./configure --with-js-lib=/usr/lib/xulrunner-devel-184.108.40.206/lib/ --with-js-include=/usr/lib/xulrunner-devel-220.127.116.11/include
And then make with the same LD_RUN_PATH:
$ LD_RUN_PATH=/usr/lib/xulrunner-18.104.22.168 make
Finally, make install CouchDB as usual and you're ok to start the CouchDB server.
Note that if Ubuntu's standard CouchDB package is also installed you may need to avoid your install clashing with it. Edit your install's etc/couchdb/local.ini and set port in the httpd section to something different. I use 15984 but it doesn't really matter as long as it's unique.