You can download the DNG converter here:
Here is an excellent video tutorial on how to use it:
Your Canon EOS Rebel T1i is supported and only requires ACR 5.4 or newer.
Since you have Photoshop CS5 you should have ACR 6.7, so either there is something wrong with your install of ACR or you are doing something wrong.
Trying to open in PHOTOSHOP RAW is completely different than ADOBE CAMERA RAW.
You need to use Adobe Camera Raw (ACR),
Just forget that Photoshop Raw even exists.It does not do what you need to do to open your CR2 files.