The upgrade works just fine. I've built an mp3 player that started out with a 16F877, then to an 18F452, and now it's running from an 18F4620.

The only problems I've encountered are a few bit positions in registers that got moved around a bit, so read your datasheets and make sure everything is accessed in the right spots.

Also, with the 18F4620, there seems to be problems with the SPI port. I can't get mine to work, so I use a software based SPI work around.

Other people will say that the newer PIC chips have problems with losing ram data, code execution problems at high speeds, locking up for no reason, etc.etc. I can say from extensive experience on a dozen or so completely different projects in various operating environments from battery powered living room types to underhood automobile data loggers to outdoor projects in the past 3 years, I haven't had any of these problems that others have had. Maybe it's because I've got plenty of bypass cap's around the PIC, maybe a steadier power supply, maybe because I read the fine print in the datasheets and take note on problems that have occurred in the past that others have learned from, I don't know.

In short, yes, the PBP code should port right over...as long as you keep track of your registers and various bit positions like I said earlier...
JDG