When you hover your mouse pointer over a folder in Explorer, Windows XP will automatically calculate the size of all files in the folder and subfolder, displaying the results as a tooltip popup. To avoid wasting CPU cycles or causing your hard drive to spin every time you hover your mouse pointer over a folder, you can disable this feature:
- Click Start, Run and type "control folders" to go to the Folder Options menu
- When the dialog box appears, select the View tab, uncheck "Display file size information in folder tips" and click OK
You can still obtain folder size via right-clicking on a folder and selecting Properties > General.