Hi mlasack,
Welcome to the HP Forums, I hope you enjoy your experience!
I understand you want to know if one of the two printers will work on you Mac running 10.4.
I will be happy to help you.
The ENVY 4500 supports 10.6 and higher.
The Photosmart 6520 supports 10.6 and higher also.
Unfortunately there are no drivers for the 10.4 for those printers.
Here are two models that will work with 10.4, the drivers are available.
The Officejet 4500 and the Photosmart D110.
Hope this helps.
Thank you for posting on the HP Forums.
Have a wonderful day!