a = 25 // a=numbers of banners
var slump = Math.random();
var talet = Math.round(slump * (a-1))+1;

function create() {
        this.width = ''
        this.height = ''
        this.src = ''
        this.href = ''
                 this.border = ''
                 this.target = ''
}

b = new Array()
for(var i=1; i<=a; i++) { b[i] = new create() }

b[1].src    = "immagini/_1.jpg"
b[1].width  = "560"
b[1].height = "330"
b[1].border = "0"

b[2].src    = "immagini/_2.jpg"
b[2].width  = "560"
b[2].height = "330"
b[2].border = "0"

b[3].src    = "immagini/_3.jpg"
b[3].width  = "560"
b[3].height = "330"
b[3].border = "0"

b[4].src    = "immagini/_4.jpg"
b[4].width  = "560"
b[4].height = "330"
b[4].border = "0"

b[5].src    = "immagini/_5.jpg"
b[5].width  = "560"
b[5].height = "330"
b[5].border = "0"

b[6].src    = "immagini/_6.jpg"
b[6].width  = "560"
b[6].height = "330"
b[6].border = "0"

b[7].src    = "immagini/_7.jpg"
b[7].width  = "560"
b[7].height = "330"
b[7].border = "0"

b[8].src    = "immagini/_8.jpg"
b[8].width  = "560"
b[8].height = "330"
b[8].border = "0"

b[9].src    = "immagini/_9.jpg"
b[9].width  = "560"
b[9].height = "330"
b[9].border = "0"

b[10].src    = "immagini/_10.jpg"
b[10].width  = "560"
b[10].height = "330"
b[10].border = "0"

b[11].src    = "immagini/_11.jpg"
b[11].width  = "560"
b[11].height = "330"
b[11].border = "0"

b[12].src    = "immagini/_12.jpg"
b[12].width  = "560"
b[12].height = "330"
b[12].border = "0"

b[13].src    = "immagini/_13.jpg"
b[13].width  = "560"
b[13].height = "330"
b[13].border = "0"

b[14].src    = "immagini/_14.jpg"
b[14].width  = "560"
b[14].height = "330"
b[14].border = "0"

b[15].src    = "immagini/_15.jpg"
b[15].width  = "560"
b[15].height = "330"
b[15].border = "0"

b[16].src    = "immagini/_16.jpg"
b[16].width  = "560"
b[16].height = "330"
b[16].border = "0"

b[17].src    = "immagini/_17.jpg"
b[17].width  = "560"
b[17].height = "330"
b[17].border = "0"

b[18].src    = "immagini/_18.jpg"
b[18].width  = "560"
b[18].height = "330"
b[18].border = "0"

b[19].src    = "immagini/_19.jpg"
b[19].width  = "560"
b[19].height = "330"
b[19].border = "0"

b[20].src    = "immagini/_20.jpg"
b[20].width  = "560"
b[20].height = "330"
b[20].border = "0"

b[21].src    = "immagini/_21.jpg"
b[21].width  = "560"
b[21].height = "330"
b[21].border = "0"

b[22].src    = "immagini/_22.jpg"
b[22].width  = "560"
b[22].height = "330"
b[22].border = "0"

b[23].src    = "immagini/_23.jpg"
b[23].width  = "560"
b[23].height = "330"
b[23].border = "0"

b[24].src    = "immagini/_24.jpg"
b[24].width  = "560"
b[24].height = "330"
b[24].border = "0"

b[25].src    = "immagini/_25.jpg"
b[25].width  = "560"
b[25].height = "330"
b[25].border = "0"

var visa = "";

visa += '<img src="'+b[talet].src+'" height='+b[talet].height
visa += ' width='+b[talet].width+' border='+b[talet].border+'>';