Can you recover a replaced file?By mistake I overwrote/replaced an inportant excel file.
If you aren't using XP you may be able to
http://www.doncaprio.com/2011/10/recover-overwritten-files-in-windows7.html
And even if you are using XP, you can still replace it, just have to do it with a script that does it before Windows loads.
Otherwise, XP will replace it in 10 seconds or so.
There is also system restore on XP/Vista/7, so if you have all your things backup up first, you may be able to use that.
* If you use Windows ME, it also comes with System Restore, but I don't think you use that...