I have a Canon T1i. Is there a setting to see through the screen instead of the eyepiece?

[Scatterbrained]

What you're refering to is called LiveView. It can only be accessed when the camera is in M, Tv or Av mode.    You can read all the particulars starting on page 105 of the manual here: http://gdlp01.c-wss.com/gds/6/0300002246/01/eosrti-eos500d-imh-en.pdf

[BrickR]

Keep in mind that AF with live view will be slower than with the viewfinder. Just FYI