Add this one to the "how did I not know about this?" file. Via the Off-Topic list, I learned that the venerable "doskey" app is still alive and well in XP. I remember doskey from the old MS-DOS days, but I didn't realize that it had survived to the present. One cool thing about it is that it lets you define macros - essentially your own command-line commands - without messing around with batch files. For example, from the command prompt type:
doskey mydocs=cd /d "%USERPROFILE%\My Documents"
and when you type "mydocs" from the command line, it will change to your "My Documents" folder. Sweet.
Full docs can be found here.