Hi Anthea,
Welcome to this Microsoft Project newsgroup
Double click on a task name to bring up the Task Information dialog and in
the General tab there is a box for you to set priorities. 1000 is the
highest (which in effect means do not level), so 1000, 500, and 0 would give
you the High, Medium and Low settings. But then so would 501,500 and 499,
or any other combination of 3 numbers! Can I remind you that thers priority
settings are only used by Project when you select Resource Levelling, and
you must also select Priority,Standard in the Resource Levelling dialog for
them to take immediate effect.
FAQs, companion products and other useful Project information can be seen at
this web address: <
http://www.mvps.org/project/>
Hope this helps - please let us know how you get on

)
Mike Glen
MS Project MVP