'Xpepius', and 'Folder Size'

Xpepius

XPepius is a free tools suite for tweaking, optimizing and tuning of Windows XP. It helps you increase performance and manage your system using various tweaks and utilities. In addition to the tweaks, the program also offers several tools (Utilities) that include a Start-Up Manager, Uninstaller, Cleanup Center (includes registry cleaner and track cleaner), Disk Cleanup, and Designer XP. Includes Various tweaks to System, Explorer, Start menu, Desktop, Drives and more; Tweaks to Enhance your security; Tweaks to Internet Explorer and Windows Media Player; Utility to edit registered application paths; Startup Manager to add, delete and edit startup programs; Uninstaller with editor of software information; Tools for cleaning registry and remove tracks from disk; Disk Cleanup utility to remove temporary and junk files from disk; Designer XP to enable new visual styles for older apps; Fully skinned and user-friendly interface; (13 available skins, animated, fast switching, fade in effects). Full HTML help system; (Detailed info about each tweak, step by step explanation about utilities). Drag and drop support; (Auto detection, multiple files support, shell link solving). And many more.

http://www.geocities.com/xpepius/

Folder Size

Folder Size Explorer Extension adds a new column to the Details view in Windows Explorer. The new column shows not only the size of files, but also the size of folders. It keeps track of which folders you view, and scans them in the background so you can see complete size of all files within the folder. It's very useful for cleaning up your disk. Once you get used to having that information available, a directory listing simply looks incomplete without it.

http://foldersize.sourceforge.net/