As Curt says, you need Camera Raw 4.4 minimum to open the XSi's raw files, and as Camera Raw 5.x should be installed with CS4 you should not need to update. When you say "cannot open" what exactly do you mean? Do you get an error message? Does nothing happen? Please be more descriptive.
It says error cannot recognize files!
This usually means you have a newer RAW file format then the Raw converter in Camera Raw. But for further investigation we do need to have more details about what file you are trying to open (from which dSLR) and what version of Bridge you are using. Also in PS check About plug in to see which version of ACR you are using.
And you are aware of the fact that all contact details are send from your iPhone with this mail? You can delete it during a short period using edit if you wish so.
You probably can not edit info if the post has been responded to. Will have to wait for a Moderator to come in and wipe personal info. [done -- if you flag a message for review, it'll be attended to pretty quickly ]
Most problems with camera raw are either you have wrong ACR version, it is in wrong folder, or there are 2 versions in the folder.
If you open a picture camera raw (even right click for jpeg) in Bridge look at the version number in upper left hand corner of window. What is that?
If you download the Adobe DNG convertor you achieve two things
1. You can save 20% of file space as DNG RAW files are compressed, but without losing any of their funcionality
2. It doesn't matter what camera you have, as you will always be able to read the DNG files.