Can I use Photoshop as an interior design software?

Since Photoshop is really for image editing, I don't really think it would be suitable for that. Although at a push, you could use it for some simple designs.

You'd be better with some vector graphics software, or even better some CAD software. If you don't want to spend any cash, why not try some open source software. Inkscape is a vector drawing application similar to Adobe Illustrator - get it here: http://www.inkscape.org/

Photoshop For Interior Design

It's hard to use Photoshop for interior design. If you want to find easy tool, you can try 4design software for interior design. It's easy to use with mouse click and can provide intuitive rendering pictures in minutes.

You can, but it would be better if you go with interior design softwares for better usability. There are a lot of free interior design software that you can choose from. I suggest you go with the HGTV Room Planner. It provides you all of the basic tools that you need to give you a solid basis for your interior design ambitions. Moreover, it gives you the opportunity to add, remove or re-size walls. You can also choose furniture and move it around.

Low-Cost Alternative:

Fluid Designer (based on Blender)

http://microvellum.com/products/fluid-designer

As a hobbyist, freelancer, or small to medium sized studio you can use Fluid Designer and Blender as a low-cost alternative to 3ds Max ($125/month) and After Effects ($20/month).

Fluid Designer by Microvellum (used with Blender)

http://youtube.com/watch?v=K_blSorT820

Architectural Visualization by Andrew Price (made with Blender)

http://youtube.com/watch?v=yJzA0IFR-78

you can make the grid with the ruler (ctrl+r) and dragging the lines out.