I need a graph similar to the Google Finance graph, seen here
http://www.google.com/finance?q=c

Basically, it needs to be adjustable based on time, and be able to compare multiple data lines on 1 chart.

I'd like to be able to enter my own data, so there needs to be a way for me (the admin) to enter data in.

Can anyone do this? How big of a project would it be? Are there any scripts available that would be able to do this?