I see no reason why a series resistor would help in case of AT89S52. There are '51 derivatives where the RESET pin is bidirectional (i.e. in case of watchdog event or brownout the mcu pulls up actively the RESET pin from "inside" - e.g. DS89C4x0), where a series resistor would eliminate possible collision - but this is NOT the case of AT89Sxx. You might still have collisitons with your programming "gadget", for which I know nothing, as you posted nothing, so I can't give any help in this regard.
Is there any problem with posting the (relevant part of) schematics (including the ISP circuit if it's permanently connected)? And the result of measurements I asked you for? It's 1 minute work to measure and maybe 5 more to report here... Otherwise, I can't quite see why did you post your original question here... Of course, it's your choice.
JW