Hi,
No, there's no PIC on any Arduino but there are (a boatload of) ATMEL chips on Great Cow Basics list of suported chips.
So, apparently Great Cow BASIC can be used with the Arduinos but to answer Hylans original question, no, PBP can't compile code for an Arduino (ATMEL MCU).
If you want a development platform "like" the Arduino but based on PIC instead (and write your code in PBP) take a look at the AMICUS18 or (a clone) the AMIPIC18. Arduino shields fit these boards physically, sometimes you need to take care of some electrical connection issues/conflicts, like with the Ethernet shield.
/Henrik.
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