What you're doing with it?
The 16C745 is not recommended for new designs, Microchip suggests the 18F2450 instead. It's pin compatible, 2x the amount of program memory, 3x the amount of RAM, 4x the amount of USB buffer memory for the same price - and your PK3 can program it. I don't know how much (if any) the code needs changing though - probably depends on what you're doing with it. Just looked at the USB module and it IS different so if that's what you're using then I understand it might no be worth mucking around if it's a proven design.

I've got the old PICStart+ somewhere, but I don't know what software will drive this decade :-)

/Henrik.