This has been touched only a couple of weeks back.

A search on 16F88 would have found...

http://www.picbasic.co.uk/forum/show...ghlight=thread

Define OSCCAL is really only for the 12 series PICs and does not set the frequency 'per se', but loads the factory calibration values to trim the simple 4MHz internal oscillator as close as it gets.

Don't forget to tell PBP the Oscillator setting you've switched into... see Define OSC in the PBP manual.