The P89C51Rx2 has a different boot/user startup scheme than Atmel (and IMHO an inferior one). A few hints:

• read the datasheet of P89C51Rx2 thoroughly; the relevant parts are around Flash programming and are reproduced in appnote AN462 (somebody please check if this is the proper number, I don't intend to dive into the crappy NXP web just to find this out) [added later: it's wrong - see below]
  
• search for NoTouch and BackDoor, both concepts (C) Erik Malund (look at his user site here and his appnote on the FlashMagic site)
  
• Atmel has a "migration" appnote http://www.atmel.com/dyn/resou...oc7605.pdf - this should be helpful to understand the differences, even if you are migrating in the other direction... ;-)
  
• if you have the parts socketed, you can salvage them in a parallel programmer (try to locate one in your neighbourhood, it's a good thing to have access to one of these); alternatively if you can put it into a board with external ROM I could send you a "bootvector recovery" utility (but it's stitched together with myself, no real guarantee)

JW

[corrected myself later] OK the proper appnote number is 461 and, basically, you don't want to clear the bootvector to other than FC (also you must not disconnect power or otherwise cancel the rather lengthy fullerase process, otherwise the bootvector might end up to be cleared to 00, too).