function preloadImg(src)	{img=new Image(); img.src=src;}
function swapPic(img,src)	{img.src=src;}
function menuOn(no)		{document.getElementById("but"+no).src = imgsOn[(no-1)];}
function menuOff(no)		{document.getElementById("but"+no).src = imgsOff[(no-1)];}

imgsOn	= ['/img/but-home-active.png','/img/but-company-active.png','/img/but-projects-active.png','/img/but-blog-active.png','/img/but-contact-active.png'];
imgsOff	= ['/img/but-home-inactive.png','/img/but-company-inactive.png','/img/but-projects-inactive.png','/img/but-blog-inactive.png','/img/but-contact-inactive.png'];
for(var i in imgsOn)	preloadImg(imgsOn[i]);
for(var i in imgsOff)	preloadImg(imgsOff[i]);