To change baud rates you would do the following.
To set the baud rate,
1. power off and then power on the scantool
2. Start hyperterminal set parameters to 9600 N81 and type in ATDP
3. You should see a response ELM327 compatible...
4. Now type ATSCS 4
the scantool will respond with OK
this will set the speed to 38400
(Higher baudrates woule need 5,6,7 - 7 being 128KBPS)
5. At this point you will not be able to type anything else as hyperterminal is set to 9600 bauds while the scantool is at 38400.
6. Shut down hyperterminal and start a new session but now set the parameters to 38400 N81
7. Now type in atdp and the scantool should respond with ELM327 compatible...
8. At this point you can issue ATWCS to save the comm speed and then the scantool will always use the higher speed on powerup
OBD II defines CAN Baudrates at 250KBPS & 500 KBPS. Most of the vehicles I am aware of use the 500 KBPS baudrates.