adding variables question -easy (for those in the know!)

[highab]

This distant rollover works:

function top*****ange()
{
	if (document.images) 
	{
		document.topbit.src=01bit.jpg);
	}
}

but how do I change it to use a variable ?

function top*****ange(name)
{
	if (document.images) 
	{
		document.topbit.src=name+ ".jpg");
	}
}

it's the right punctuation around the name+ .jpg that's my problem....

any help would be much appreciated