how to amplify a 3v supply into 4 or 5v

supply coming from rf receiver, going into pic

Aren't those things open collector (meaning that the output High will depend on the Vcc)?

Also, you could always put a transistor as a switch, connect the output of the RF receiver to the base through the resistor, and take the output from Collector.

To figure out the values of resistors:
Base resistor:
Let's say you want 1mA at collector, then you'll need 10uA at base (for a general purpose transistor, as 2N3904). Then, (3V - 0.7V) / (10 * 10^-6) = 230K. This is your Rb.
The collector resistor (Rc) would be:
5V / (10^-3) = 5K.

The intput is where you connect your RF module and output goes to microprocessor.

But again, look at the datasheet of the RF module, it's supposed to have an open-collector output (you just put a resistor from Vcc to output and that's it).

Good Luck,
TI|CP

my input is from an rf receiver and is pulsed on and off from 3v to 0v

will the transistor generate the same pulsed output? after the input is passed through the base?

The output from the circuit given above will be inverted.
i.e. 3V to 0V in will give 0V to Vcc out, Vcc being the value of the transistor's collector supply.
If you want 5V out you must have a 5V supply.

Take a look at the switching voltages on the PIC datasheet it. Often a 3V signal will work fine on a 5V input.