You can find a lot of information on replacing the focusing screen
when you google for haoda focusing screen. Here is a good link:
http://www.camerahacker.com/Tools/Installing_Haoda_Screen.shtml
Now, what I did was to take a focusing screen from an old film body
(an Olympus OM-G in my case) and file it down to size, and around
the corners I also had to file down the thickness., so the split
prism would be in the exact position. (You'd be amazed how much
1/100mm matters in thickness.)
It was a bit of work, but not all that hard. It really helps a lot
in achieving or at least confirming correct focus on the 300D. I
wasn't so sure about keeping that camera for a long time, until I
replaced the focusing screen. It makes me much more confident about
focus. In fact, I sometimes wish I had not sold the optically
excellent Signa 18-125. I sold it because with my camera it could
not focus correctly (mostly at the long end), but with the focusing
screen I would immediately notice and be able to correct it.