Not sure if this will help, but I made a full 2004 roster set for OOTP4 as well as an all time roster set for OOTP4.
I do not know if OOTP4 and OOTP3 rosters would be compatible, but it's worth a try.
Just go to my website (the link is in my signature) and feel free to try them.
Enjoy!!
SPeeDy
Creator of sports sims rosters.
Available for download at my website:
http://www.geocities.com/speedy_sports_sims/index.htm