Most modelers use a package like Maya, XSI, or 3DS Max for modeling and UV'ing, ZBrush for detailing, and Photoshop for texture creation.
My personal toolset is Maya/XSI for modeling/UV'ing, Zbrush for normalmapping the highpoly if there is one, Photoshop/Paint.NET for texturing, and XSI for rigging/animation since it's the only tool that seems to be compatible with Source engine animation.
Since you seem to be new, I would recommend to you XSI Mod Tool 7.5 for modeling and Paint.NET for texturing since these are both free programs and therefore you won't be at a loss if you decide you don't like modeling or it's too difficult.
I know that Spider has a fantastic head modeling tutorial (I'm using it, it has some fantastic techniques) which I'm sure another dev can come by and post a download link to.
