If the performance counters are disabled, rather than missing or corrupted, you could use exctrlst from click here to re-enable them. This program is mentioned half way down madboy's link.
Within the program, click on each item and make sure the "Performance Counters Enabled" box is ticked for each one. (Although exctrlst is for Windows2000 I've used it on XP when some performance counters were disabled.)
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