Height Trouble!

Wasnt sure where to post this so I posted it in both sections! I apologize for the double post!

I want to use a Javascript to dynamically change the height of this div statement

<div id=DWelcome style='position:absolute; visibility:hidden; font-family:arial; font-size:10pt; width: 450; height: 250; Z-Index: 1; clip:rect(0,450,250,0); background-color:#CCCCCC; layer-background-color:#CCCCCC'>
<P Align=Center>
<b>Welcome</b><BR>
</P>
</div>

I figured something like this would work

<script>
function h(){
if(document.body.width=600){250}
if(document.body.width=768){350}
}
</script>

and the do the following
<div id=DWelcome style='position:absolute; visibility:hidden; font-family:arial; font-size:10pt; width: 450; height: h(); Z-Index: 1; clip:rect(0,450,h(),0); background-color:#CCCCCC; layer-background-color:#CCCCCC'>
<P Align=Center>
<b>Welcome</b><BR>
</P>
</div>

but it doesnt work!

The other thread is at http://www.codingforums.com/showthread.php?s=&threadid=17048