When I debug a script which use shared memory just after I call the function shmop_read the task phped.exe take 99% CPU and it's memory usage change very often (at each refresh of the task manager it goes from 70mb to 110mb)

there isnt' any problem with shmop_open. I try to read 131072 bytes from the shared memory. After I've done the unset of the memory read the cpu usage of phped come back normal.

Any idea?

I use php 4.1.0, win xp pro and eaccellerator

I would highly recommend you remove all caching-accelearating stuff from the development server. They all have nothing to help you debugging your scripts and only may cause problems with performance, memory consumption and debugging.