I realize that this is very old, but I would like to point out that MXF files can be read/used by Premiere CS5.5... but not all MXF's are created equal. Our Canon MXF's come in just fine, however everything we shoot on our Grass Valley Infinity cameras can not be imported natively. For that we've had to either use Edius to import and convert the files to Premiere friendly files or purchase the Main Concepts MPEG 2 plugin. With that plugin the MXF files can be imported & edited in CS5.5.
Not sure about any of this in relation to CS3 though (assuming you haven't upgraded in the last 3 years).