I need help on figuring out what formula to use.

Here is what I am trying to do:

My sales reps need to submit a date of when they found a prospect.
With that date, they also inform me of what priority they are based on
a scale of 1-5. Each priority has time frame on which I would like
them to move the prospect to the next phase, ( for example Priority 1
is 0-30 days). I would like to insert a column telling me how long the
prospect has been in the first phase and if it has gone over the time
alotted I would like for it to change color. So I need the formula to
include the priority and the time frame, as well as the number of days
it has been since the sales rep placed the prospect. If my description
is confusing here is an example.

Date Entered Priority Days In Phase 1
8/15/09 1 5 (If Todays
date is 8/20/09)


Please Help