Depends on what you want to clean the hard drive for, and how you want to get rid of the information. If you need to free up space on the drive, Start> All Programs> Accessories> System Tools> Disk Cleanup. If you want to clean up the hard drive because you want to sell the PC, or plan on giving it to someone, you have to realize that just because you delete files, that does not mean that someone who knows what they are doing can't find them.

Here's the problem: An index of files is maintained for the hard drive, telling it where things are stored. When you install a file, especially a big one, it is scattered around the hard drive in bits and pieces. On your command to open the file, the hard drive checks the index, then gathers the pieces and reconstructs them.

When that file is deleted, the links between the index and the file disappear. That tells your system that the file is no longer needed and that hard drive space can be overwritten. But the deleted file remains on your computer. Only when it is overwritten do you begin to be safe. Even then, a specialist might be able to recover the old data.

Assuming you just deleted everything in preparation for saying goodbye to your PC, it is unlikely that the sensitive information has been overwritten. It's still sitting there, and anybody with a shareware program could find it.

Reformatting a disk prepares it to accept a new operating system. It also wipes out everything on the hard drive. That's your goal.

Past versions of Windows (through Windows ME) allow you to create a start-up disk. You'll need one to reformat your hard drive. Click Start > Settings > Control Panel. Double-click Add/Remove Programs. Click Start-up Disk. Click Create Disk.

On Windows XP, you'll need to download the disk information. Go to BootDisk.com and click "DOS — Windows 9X/NT4/2000/XP Excellent Bootdisks." Download the Windows XP Custom Install Disk and save it to a floppy.

On all systems, shut down all open programs. Restart the computer with the floppy in the A: drive. At the A: prompt, type Format: C. Answer "yes" to the warning; you want to wipe out all the data. When the reformat finishes, put the Windows installation CD in the CD drive and remove the floppy. Restart and re-install Windows.

Reformatting will keep most people out of your old files. But specialised shareware exists to reclaim files after reformatting. If you do not know who will get the computer — or you do know and you don't trust them — stronger measures are required.

If you don't know much about computers, this might be easier than reformating the drive. There are several programs that write gibberish to the hard drive. They promise that nobody will be able to find your files after the software is utilised.

Norton's SystemWorks includes an application called Wipe Info. OnTrack's DataEraser offers a similar feature, as does Jetico's BCWipe. There are more such applications on the Internet.

You can leave the operating system and other files on the hard disk, if you want. These programs can be set to overwrite only the unoccupied areas. The process can be slow, because they write to the disk repeatedly. You might want to run it overnight.