var im1_off=new Image();
im1_off.src="images/bt-travel-software-off.jpg";
var im1_on=new Image();
im1_on.src="images/bt-travel-software-on.jpg";

var im2_off=new Image();
im2_off.src="images/bt-web-developement-off.jpg";
var im2_on=new Image();
im2_on.src="images/bt-web-developement-on.jpg";

var im3_off=new Image();
im3_off.src="images/bt-bespoke-developement-off.jpg";
var im3_on=new Image();
im3_on.src="images/bt-bespoke-developement-on.jpg";

var im4_off=new Image();
im4_off.src="images/bt-customer-portfolio-off.jpg";
var im4_on=new Image();
im4_on.src="images/bt-customer-portfolio-on.jpg";

function offImg(a)
	{	
		if(document.images)
			{eval("document.im"+a+".src=im"+a+"_off.src");}
	}
	
function onImg(a)
	{				
		if(document.images)
			{eval("document.im"+a+".src=im"+a+"_on.src");}
	}