I replaced the original infrared blocking filter in the Canon XSi (450D) with a filter sold for doing astrophotography. The replacement filter also opened up the camera for daytime infrared photography. Detailed instructions for the procedure are here:

http://ghonis2.ho8.com/rebelmod450d1.html

Daytime infrared test images are here:

http://ghonis2.ho8.com/rebelmod450d14a.html

For the test imges I used the kit lens that came with the 450D: the Canon Zoom EF-S 18-55mm 1:3.5-5.6 IS. It is threaded for 58mm and that is the size of the HOYA R72 filter I use.

When I modified a Canon 300D a few years ago for infrared/astro imaging, I replaced the IR block filter with optical clear glass, that is better for infrared. The Baader replacement filter I used for the 450D replacement is an IR blocking filter but is allowing enough infrared passage to be useful as a daytime infrared camera. The live-view focus mode of the 450D is a godsend for focusing infrared/astro and is the main benefit of this new Canon DSLR.

Gary