first u should write another vb program that send and / or recieved data as your at89c52 should do
to verify your PC side is correct , and do the same for your at89c52 , just for sure that you got both side in right direction then you are ready to conect your at89c52 to PC, but it's only just get you to the start point , still have some small detail need to be care of , post and let us know when your pc & 52 can talk to each other
have fun
Chris Chang