Assuming the Rules don't change in the meantime, your brother should be eligible for ILR after five years on a work permit. Time as a student doesn't count, except toward ILR after ten years.

paul

When my brother came in May 2000 he was granted permission to work because his wife was a student. Should he disregard that period upto September 20004? Because in October 2004 he was granted another work permit along with his wife, after she graduated from nursing.

Which period  should he count his 5 years for ILR? Is it from May 2000 or does he count it from October 2004 when his wife was also granted a work permit?

This is how it happened for me and my wife, too:  student (me), then changing over to a work visa. 

Your brother came in as a dependent on his wife's student visa, not as a visa holder in his own right.  Therefore, the same basic terms apply as applied to hers:  student time does not count towards settlement, and neither does time as a student's dependent.  (If dependent time counted, it would be very easy to scam the system.) 

Your brother should count from October 2004 for his ILR because that was the first time he was in the country on a settlement-track -- but, assuming there was no break in residence, he may count from 2000 for citizenship. 

My brother came here in May 2000 on a student wife visa. It allowed him to work until October 2004. His wife graduated as a nurse 2004 , she and my brother were both granted work permits valid until October 2008.

 Does he qualify for ILR? And which date is it valid from?