They are rather poor quality AM (OOK) modules so don't expect good results. You probably find the receiver is picking up data even when the transimtter is unpowered.
Things to try:
1. drop the baud rate down, they are 'rated' to 9600 bauds but I suggest 2400 as maximum.
2. try inverting the transmitted and received signals, this will keep the transmitter running longer so interference at the receiver will be quietened. Wire the inverters at the TX module input pin and at the RX module output pin, not the PC side of the MAX232s.
3. check the modules work at the same frequency and you don't have one at 315MHz and the other at 433MHZ!
Brian.