Hello briandear,
Welcome to the HP Forums! I hope you enjoy your stay!
I understand the microphone is not working since you upgraded your operating system. I will do what I can to assist you! I searched the product and determined that there are no supported Windows 7 drivers, as indicated here: HP Pavilion dv1000 Notebook PC Drivers
As an additional suggestion, there are troubleshooting steps you can attempt. These steps can instruct you through setting up the microphone. However, I cannot guarantee these steps will work, since the operating system is not supported.
If you want to attempt these steps, you can locate them here: Resolving Microphone and Line-in Problems (Windows 7)
Please let me know your results. Thanks for choosing the HP Forums. Have a great day!
Mario