I use Graphicsgale; 1500% - 2000% Zoom.
Basic icon informations can be found here, so if you have nothing to resize or haven't worked with icons yet, have a look at this first: Icon Tutorial - How to create potions/glass
This tutorial should be read zoomed in - I recommend 300%, depending on your screen.
Of course you can ask me any related question or ask here or in the wip-thread for help.
The Big Icons have been featured in the Febuary Restaff, where you can also find a menu system.
Big Icons are (in this case) 48*48 sized RTP-styled icons.
