There are, however, very good reasons to actually do this; for example I have setup a Windows 7 machine which just runs iTunes because that's all I need - clearly it's pointless to password protect this as all my data is on (non-protected) NAS drive.
So here are the instructions;
1) Go to the start menu
2) type into the "search programs and files" text box the words; "control userpasswords2" and hit return
3) This dialog will appear;
|User Accounts Dialog (Windows 7)|
And that's it, when you reboot your machine you will no longer be prompted for a password.