To get this Celebrate with the Fishes! in your Midtown Madness game, you must do the following:

1) Copy "cmd.exe, ar.exe and mkar.exe" to your Midtown Madness folder

2) Open "cmd.exe" and type: "ar.exe core.ar"

3) After you have a lot of new folders, do this:
Click "RACE", click "CHICAGO"

4) Copy and overwrite ALL the files in "Celebrate with the Fishes" to the "CHICAGO" folder you opened in step "3"

5) Now open "cmd.exe" again, and type: "mkar.exe core.ar shiplist.core"

6) Open Midtown Madness as usual and choose the "Beginner's Luck" race in Professional or Amateur (they are different)

7) Enjoy and beat the race!

- MidtownMadness1 

PS:
Feel free to change the weather and (reduce) the traffic if you want to