hi Johnson
of cource,u can retarget a C source code originally written for 8051 microcontroller to PIC.
m using pic from 16F series n its working fine with some 8051 c code.in pic ,there are some advance features are available( in comparison with 8051).like built in adc,capture/compare module etc…so when u are using ports as i/p or o/p, u have to disable all alternate features to use pin for particular operations.
also u have to enable /disable different reset fun of pic according to ur appl..also choose perfect oscillator for program………..
besides following all this, make initialization/declarations as per syntax of different PIC.
best luck.