From
http://docwiki.gumstix.org/Buildroot_on_Ubuntu:
* build-essential - this installs a complete build environment
o This gets you all the necessary packages to build software, like gcc,autoconf,automake,libtool etc.
* openssl-dev (on Ubuntu 7.04 or 7.10, libssl-dev is needed instead)
* libncurses-dev
* bison
* flex
* texinfo
* zlib1g-dev
* gettext
* autoconf
That being said, I just installed Buildroot on Hardy and it checks for the necessary packages at the start of the build, alerting you of any needed packages. If you're getting error messages further into the build, you may have other problems.
Alex