Chart using 2 columns of date information

Hi,

I am currently using Excel 2010 and have a question about creating a chart using 2 columns of date information.

I have one column with dates for when we have created a new user account and another column when that account was requested by their manager.

I would like to create a chart that displays the number of days between the two dates.

Examples. An account was requested today and the person starts tomorrow. This would be 1.
An account was requested today but the user started 3 days ago. That would be -3.

So the final result would be a pie chart showing that out of all the new user requests, a certain number were made 1 day in advance, some were made the same day, some were made 14 days in advance, etc...

Hopefully someone can point me in the right direction.

Thanks!

Derek