How much RAM/memory do I need for photography?

I'm currently using Photoshop CS6 and Lightroom 4 with my Nikon D5100 on my Toshiba laptop, but I've been thinking about buying a desktop for easier use.

1 GB is good enough. 4 GB is ideal

Really not to much unless your doing rendering or advanced modeling ram should be enough to upgrade

most laptops can have up to 4x2gb 204 pin or 2x2gb 204 pin

the speed and type depends on your toshiba

you can find out
by looking at the far right corner there will be something like

c655d s5136 satalight