Trackpad at login

I tried searching the forum and couldn't find an answer to what I am looking for so here goes -

I have a 17" MacBook Pro and when I get to the login screen during power-up the trackpad moves the cursor around but I can not select a user to login. If I have a USB wireless mouse connected, it will work. But 99.5% of the time I use only the trackpad. My login is the first on the list so normally I would press the down arrow to select my username and press enter to get the password prompt. I'm running OS X 10.6 (Snow Leopard) but it worked this way with OS X 10.5 (Leopard) also.

Is there some setting that needs changing to get this to work?

mine is set up to tap in the system preferences for my account, so i assumed that was how i make it work during bootup for my macbook pro. i'm also using 10.6, and it works fine for me, and did so in 10.5 as well.

Maybe I should clarify a little more. The enter button at the bottom of the trackpad will select whatever the cursor is on. But I can not do a tap (or double tap) on the trackpad to select the user.

Note:
Making the change detpenguin suggested didn't make any difference.