I am painting the wall in my livingroom and would like that sort of streaked mexican unfinished look. How do I do this?

Good paint stores can show you faux finishes. Basically you paint the wall the base/primary color. Later you come back and streak with a glaze finish. A rag, brush or even a crumpled plastic bag can be used to create some neat designs.

I just did this in 2 of my rooms myself- paint the wall a lighter solid color then use a glaze with a darker color mix it 4 parts glaze 1 part paint (or what ever your glaze bottle tells you) then take a brush and put a bunch of x's on the wall and take a rag and swish it around- do it in 4x4 sections so the paint won't dry
Hope this helps- something else you might want to try is use joint compound and paint it it will give you that spanish stucco look