I would recommend you use the CLI (Command Line Intereface) client because it is much more efficent and faster in comparison with the GUI/Screen Saver version which uses alot of your CPU cycles to process the graphics. The instructions to set it up can be found here:
At the top of the menu you will see "Join." Click it and you then enter your e-mail and password.
Feel free to ask any questions if you have trouble setting up SETI Spy + SETI Driver or signing up. I know it's a bit more complicated than Folding but you only have to do the sign up at Berekely once and from then on all your WU are included in the Overclockers.com SETI Team.
Well just to let you know, I like the screen saver anyways, even if it isn't as effecient. I leave my computer on all the time and I just like using the SETI screen saver...I like watching all the info and such. As for the info about joining the team, thanks. I am setting it up right now. I used to be into folding, but I find the idea of contacting / finding aliens to be much more interesting.