Q: Reading of an older dvd

Be more specific.  All you are making is a statement.

Ok.  Well there is no such thing as a MacBook Pro G4.  You are sure it is a MacBook Pro?  Also, what type of DVD's?  Home movies, commercial DVD's (Movies, Audio CD's etc).  What happens when you put them in?

No MacBook's have "G" in the title, and certainly can't run Lion.  Those notebooks would be made pre 2006..  Go to >about this mac and see what it says about the processor as an fyi.  Anyway here are instructions that may help:

The drive accepts discs but they do not mount or are automatically ejected

1. Check the disc's surface for scratches and dirt, since these things can prevent the disc from appearing on the desktop.
2. Reset the Power Manager (PMU) or System Management Controller (SMC).
3. Ensure your drive can read the specific type of disc being used. For example a "combo drive" can read a DVD-R and burn a CD-R however it cannot burn a DVD-R. The utility System Profiler may provide additional information regarding what media your computer supports.
4. If the discs continue to not be recognized, please contact Apple, contact an Apple Authorized Service Provider, or make an appointment with an Apple Retail Store for additional troubleshooting, evaluation, or service.

source: http://support.apple.com/kb/ht2801