Any way of benchmarking scripts on the fly?

Is there any way at all to find out how much memory, how much CPU time etc that a particular script takes up? Most of the time when a buggy script is running out of control all we can see is the httpd daemon's or the mysql daemon's stack space spiralling skyhigh... but since it's our production server there's no way of finding out what the heck's happening exactly... Would be grateful if anyone who has found a way to track any script's resource usage accurately... any way is possible, be it at the script-level, DB level or OS level... on that note, is there also a way to attribute which mysql thread was called by which php script... sounds outlandish at my limited level of knowledge... but i'm just trying desperately to find out how I can keep tabs on what our scripts are really doing... Thanks Wong