How to switch on microphone?????????/ - HP Pavilion dv1000 Notebook

First, confirm your laptop has a microphone. I am assuming, as you have posted your question, that it does.
Go first to your Control Panel, switch to classic view if you are using XP and small icons if in Vista or Windows 7. Look for some icon such as Sound or Sound and audio devices and click to enter it.
Now here is some divergence in methods.
XP
Enter the tab near the top of the window labeled as Voice. In the Voice recording section, confirm that there is a Default Device. If there isn't, click the drop-down arrow and choose on if there is one available. Sadly, if there is not, then I do not know how to help you. My expertise lie more in Vista and 7.
Vista & 7
Once inside of Sound, enter the Recording Tab and look for some type of microphone. Double click on the Microphone and at the bottom of the screen, there should be a "Device Usage" area and click the box next to it and choose "use this device (enable)" and click ok.
Hopefully one of these two methods should get your microphone working. I apologize if it doesn't. More information on your part may be helpful.
One last side note. There are two jacks on most laptops. If you are using an external microphone, you may be plugged into the output jack as opposed to the input.