For OpenOffice, the install is really very straightforward. First, your going to want to have a read through the OO
install documentation just to have an idea of what to expect. You are probably going to want to set this up as a multi-user installation, even if you are the only one using the computer. It ends up being a kind of two-step install. First, become su and then install the program. Second, drop back to being your regular user and install as local. This second step tends to just create a few directories and files in your home directory.
But in general, starting the install is as easy as dropping into the directory that was created when you unzipped and type
./install. You do need to have X running when you do this, so open up a terminal in your X environment and use that.
As for SETI, all I can say is I don't have email set up on my Slackware box and seti installed and runs just fine.