A few questions:

1) What Fz xtal and what value "pi" filter caps.

2) What is the voltage the are the parts powered with.

3) What level is found at p3.0(RXD)/p3.2(INT0) prior to the application of stimulus.

3) are the port pins in question used as serial and interupt or as gen. purpose port pins?

4) As with Erik what are you using to monitor the xtal.

5) If you monitor ALE what do you see prior-during-after stimulus.

regards,
p