To upgrade to OpenOffice 3.2.1 in Ubuntu 10.04 you need to go to System > Administration > Software Sources and on the Updates tab, make sure you have the "Pre-release updates (lucid-proposed)" option checked:
Then simply run:
sudo apt-get update sudo apt-get upgrade
Or wait for the Update Manager to prompt you with the OOo 3.2.1 update.
Important: the proposed repository is created for a reason: packages in this repository might not be stable.