Make sure your saving it as a DDS file here are some settings to use...

If you are new to making courts I have a court template here
http://www.mediafire.com/folder/16jtf3m ... _TemplatesDownload the template and the f000.iff file. Make your court and save it as a DDS.
Once you have it saved drop the dds in the f000.iff archive and replace the file big76ers256.0200976aa730f40b.dds Then rename the f000.iff to the floor you are looking to change. Throw it in the modded folder and thats it.