Here are the steps.
1.) I first create my portrait using Photoshop. 256x256. For Joe Nathan I name the file nathan.ddsfor example.
2.) Now for size of the file. This step is crucial or the portrait will look terrible in the game. For this step I take a folder with nbamodtool and a COPY of the portrait IFF. For this example I will use Joe Nathan. Use Ty's editor to look up his ID number for the roster you are using. His number is 1729 for me.
3.) Open up the copy of your portrait iff. You need to import nathan.dds into any slot (doesn't matter which one) and export it back out as 1729.dds
4.) nathan.dds was 87,536 bytes in size and the resulting 1729.dds is 87,520 bytes. As I said this step is absolutely necessary.
5.) Now for installation. Create a folder called portraitand a folder within the portrait folder called 1x. All numbered dds files go in the 1x folder. For example portrait-->1x-->1729.dds. This allows for one or hundreds of portraits to be installed. After placing all completed files in the 1x folder take 7zip and createportrait.7z
6. Install Total Installer Thingy for 2K10. On first setup it asks where your MLB install directory is and so forth. Just follow the directions. Click the ... button and load portrait.7z. Then click the start button. All portraits should now be installed in the game.