Hello,

I am sure you must have read the Intel PCA cook book which is available as a PDF on the left in the "links"
It gives lot of good tips on measuring pulse widths, periods and the lot.

As Oyvind ( I dont know how he got the crossed O )suggested, you have to somehow synch. your measurement with an edge of the incoming pulse. However you should note that the number of counts per pulse must be atleast in the range of say 100 or more to get reasonable resolution.

Raghu