Hello mate,
http://www.sopl.info/ this is the link that houses links to this forum and the league Trainer's Office Manager or TOM.
http://www.sopl.info/sopl/tom10/main.php or this is the actual link for TOM
Go down to other and click register for TOM, once you have done this you can start uploading horses. By using the stable menu.
I do not advise doing this as of yet as I'm sure you are aware if you read the forums that the league is not due to start as of yet due to TOM being changed for this season. If you read the other posts you will also see notes on how to go about exporting your horse, resetting their ratings, how to trial in the construction kit (what sort of times are good for the league etc, I find this takes the fun out of racing online though!).
Need any other advice on the stuff above or anything else then leave a comment!