This is the original default roster that can be found in a fresh installation of NBA 2K11 PC. It's provided here for the convenience of modders who may want to use it as a base, without reinstalling the game to get it. Notably, it has career stats for players like Allen Iverson, Stephon Marbury, and other veterans, which were blanked out when they were removed from the active rosters in subsequent updates. Note that it's also missing some players who were added and are available in the final official roster update.
Unzip the file to your Saves folder. It will then be available to load in-game.
XP/VISTA USERS: Go to the Start Menu and click Run. Type in %appdata% and press Enter. Then click 2K Sports, then NBA 2K11. Here you will find a folder called Saves; this is where you need to extract the files.
WINDOWS 7/8/10 USERS: Type %appdata% in Search and press Enter. It will take you to your Roaming folder, where you can click 2K Sports and then NBA 2K11. Place the files here.
If you're looking for the final official roster update for NBA 2K11, it's available here