Photoshop is costly and need huge memory of computer. It takes more than fifty percentage of memory. But these softwares takes only small memory and giving good performance. we may see useful three softwares to open the photoshop psd files without having photoshop software.
This is a good software alternative to photoshop. Generally this software have not ability to open the psd images. On the other hand, a photshop plugin for this software can make the psd viewing and editing. First download and install the Paint.net software. Then download the plugin for the photoshop, and put that plugin file to Paint.net's Filetypes folder. After putting the plugin, you can view and edit the psd files in Paint.net
http://www.4shared.com/get/R9wH-POu/PhotoShop.html (Photoshop Plugin)
Gimp is a great alternative to Photoshop. It has all of the functions like as photoshop software. This is an open source program automatically open the psd files and allows to editing the images. This software is cost free and effective one.
This is a light weight program to modify the images fastly. It has a great capablity of opening the most all types of images. But you can view the psd images and you cant edit the photoshop images on this software.