It is possible to open and edit a .psd file without the use of Photoshop.
With the help of a little software and its plugin, we can open and edit psd files.
This software is called
Paint.NET. This is not a link, that's what the software is called (perhaps to differentiate it from the regular Microsoft Paint).
Okay, I am going to give you it's download link and that of the plugin:
Download Paint.NET (3.5MB)
Download the .psd plugin (20KB)
Requirements: Windows XP/2003/Vista/Windows7/XP64/Vista64/Windows7 64
.Net Frameork
License: Freeware