if (document.images) {
//active images
bio_button_on = new Image();		
bio_button_on.src = "gfx/icons/bio_bv_button1.gif"; 
press_button_on = new Image();		
press_button_on.src = "gfx/icons/press_bv_button1.gif"; 
gal_button_on = new Image();		
gal_button_on.src = "gfx/icons/gal_bv_button1.gif"; 
mus_button_on = new Image();		
mus_button_on.src = "gfx/icons/mus_bv_button1.gif"; 
media_button_on = new Image();		
media_button_on.src = "gfx/icons/media_bv_button1.gif"; 
down_button_on = new Image();		
down_button_on.src = "gfx/icons/down_bv_button1.gif"; 
conc_button_on = new Image();		
conc_button_on.src = "gfx/icons/conc_bv_button1.gif"; 
shop_button_on = new Image();		
shop_button_on.src = "gfx/icons/shop_bv_button1.gif"; 
comm_button_on = new Image();		
comm_button_on.src = "gfx/icons/comm_bv_button1.gif"; 
apgar_button_on = new Image();		
apgar_button_on.src = "gfx/icons/apgar_bv_button1.png"; 
org_button_on = new Image();		
org_button_on.src = "gfx/icons/org_bv_button1.png"; 
uman_button_on = new Image();		
uman_button_on.src = "gfx/icons/uman_bv_button1.png"; 

//inactive images
bio_button_off = new Image();		
bio_button_off.src = "gfx/icons/bio_bv_button.gif";  
press_button_off = new Image();		
press_button_off.src = "gfx/icons/press_bv_button.gif";  
gal_button_off = new Image();		
gal_button_off.src = "gfx/icons/gal_bv_button.gif";  
mus_button_off = new Image();		
mus_button_off.src = "gfx/icons/mus_bv_button.gif";  
media_button_off = new Image();		
media_button_off.src = "gfx/icons/media_bv_button.gif";  
down_button_off = new Image();		
down_button_off.src = "gfx/icons/down_bv_button.gif";  
conc_button_off = new Image();		
conc_button_off.src = "gfx/icons/conc_bv_button.gif";  
shop_button_off = new Image();		
shop_button_off.src = "gfx/icons/shop_bv_button.gif";  
comm_button_off = new Image();		
comm_button_off.src = "gfx/icons/comm_bv_button.gif";  
apgar_button_off = new Image();		
apgar_button_off.src = "gfx/icons/apgar_bv_button.png";  
org_button_off = new Image();		
org_button_off.src = "gfx/icons/org_bv_button.png";  
uman_button_off = new Image();		
uman_button_off.src = "gfx/icons/uman_bv_button.png";  

}

function imgOn(imgName) {

if (document.images) {
document[imgName].src = eval(imgName + "_on.src");
}
}

function imgOff(imgName) {
if (document.images) {
document[imgName].src = eval(imgName + "_off.src");
}
}