FAST FORWARD'S HELP FILE Rob Pegoraro

QI'd like to use an old Logitech webcam with Skype on my iBook. But this camera's system requirements don't mention Mac use. Is this possible?

AAlthough most Mac laptops and desktops feature built-in webcams, users with older machines -- or new Mac mini and Mac Pro desktops -- have a couple of options if they want to plug in a cheap, third-party webcam.

If the non-Apple camera supports a standard called "USB Video Class," and the Mac in question runs OS X 10.4 or newer and has been patched with Apple's latest system updates, the camera should work on its own. Those versions of Apple's operating system automatically recognize USB webcams meeting this specification. How will you know which models do? The easiest way is to look for a "Certified for Windows Vista" logo on the camera's box.

With older webcams, try the free, open-source Macam. This download (http://webcam-osx.sourceforge.net) includes a standalone program and a QuickTime helper file that allows the Skype Internet-calling program to use a USB webcam. This software worked as advertised on a MacBook, where it instantly recognized an old Logitech camera.

What does it mean when somebody puts a number sign before a word in an online post?

That's called a hashtag, for the hash mark preceding the word (right, yet another name for the symbol we also call the number sign and the pound sign). People on sites like Twitter use these labels to make it easier for others to spot their postings.

For example, many people Twittering about this year's Consumer Electronics show used the hashtag #ces09 to identify their updates. You can see a list of popular hashtags at http://hashtags.org.

Rob Pegoraro attempts to untangle computing conundrums and errant electronics each week. Send questions to The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or robp@washpost.com. Turn to Thursday's Business section or visit washingtonpost.com anytime for his Fast Forward column.