1) Extract "MBP3D" folder to your "models" folder

2) In your Ring Racers folder, open models.dat and add these lines to the bottom: 
AISHACLANCLAN MBP3D/KAISHA.md3 3.0 0.0
MINAHOLLOWER MBP3D/KMINA.md3 3.0 0.0
SUMIREKANZAKI MBP3D/KSUMIRRE.md3 3.0 0.0