Go to your GTAVC Folder, and go to the folder mss
in there you make 2 folders, 0.3z & RC2
Place the vc-mp.flt file (which is in the mss folder from gtavc) into the 0.3z folder
Then copy the vc-mp.flt file from the mss folder in your RC2 installation dir, and place it into the RC2 folder.
When you want to play 0.3z,
copy the vc-mp.flt from the 0.3z folder (in your gtavc dir) into the mss folder from gtavc
When you want to play RC2,
copy the vc-mp.flt from the RC2 folder (in your gtavc dir) into the mss folder from gtavc.
Peace of cake