Logos:
C:\Documents and Settings\[username]\My Documents\Sports Interactive\OOTP Baseball 2007\data\logos
Rosters (and other games in folders with names ending in .lg):
C:\Documents and Settings\[username]\My Documents\Sports Interactive\OOTP Baseball 2007\data\saved_games
Quick Starts (games in folders with names ending in .quick):
C:\Documents and Settings\[username]\My Documents\Sports Interactive\OOTP Baseball 2007\data\quickstart_games
Templates (files ending in .wtp):
C:\Documents and Settings\[username]\My Documents\Sports Interactive\OOTP Baseball 2007\data\world_templates
More help with mod installations:
http://web.mac.com/sixwilsons/OOTPMods/Help.html