It seems that the PC Modifications for Unreal Tournament III aren't working at the moment on the PLAYSTATION 3. In addition, the URL provided at the bottom of the "My Content" page does not work it is a dead link.
Josh Adams chimed in on the situation on the official Epic Forums.
"Hmm, sorry about the dead page. I'll get that looked into.What seems to be odd is I'm pretty sure I remember someone at Epic saying that PC modifications will work on the PLAYSTATION 3 off the bat.
However, the PS3 mod tools aren't quite ready yet. We are working through some final legal/release issues.
When it's ready, you will need to download the latest PC patch and another PS3 Mod Tools "patch" that adds the full PS3 mod support to the PC version.
You will have to cook your mods for the PS3 specifically. You will also need removable media (memory card, USB drive, etc) to transfer the mod from your PC to your PS3.
We will have the tools ready ASAP!!"
[Via Epic Forums]