Repeated Query Execution - Strange Behavior

[Yongu Pongu]

Hi,

I am running a select query on a table with very large data through MySQL control
Center. MySQL version is 4.1.
Some times the query returns data in 5 minutes but some times it takes 10 minutes.
There is no consistency in the behaviour, some times it takes less time 1st and then more time and again less time.
Repeated execution on the query gives different performance figures.

There is no other process running on MySQL server which can affect the performance of MySQL.

Are there any settings on the MYSQL databse which can be modified to get result fast always?

Thanks in Advance.

-YP