Ok I'm going to have to say.. good point Curt, it's not a small change.. but tinjaw is right.. if the programs follow some guide lines, they should retrieve the correct path to the users' folders, and not use any hardcode paths at all..
And as for your annoying username problem, you can either change the display of it (logon, start menu) via the User management in Control Panel. This doesn't change the \Documents and Settings\Username to the new name, it merely changes a few locations that displays the username.. If you're fine with this, then do that..
Other wise if you want to completely remove the username, just create a new user (which will be your new account), copy all the \Documents and Settings\OldUserName to your .\NewUserName.. After you have copied all your old username settings to your new username.. You can assign admin (well you should have done that when you created the new account) priv's to your new account.. Then delete the old username..
tinjaw: I know about TweakUI XP
Do I need to repeat my self.. Nice screen shot though