Using onClick to load new page NS + IE

I am currently working on making legacy Javascript code written for IE work also on Netscape (v6)

Most of the code seems fine, as the amount of DHTML is minimal. However, the following code snippet works with IE and not NS:

<input type="button" value="Log on" onClick="open('../cgi/mycgi.pl?VAL1=xxx&VAL2=yyy', '_top', 'menubar,toolbar,location,scrollbars,resizable,status')">

However, replacing this with the following code works fine with both browsers:

<input type="button" value="Log on" onClick="location='../cgi/mycgi.pl?VAL1=xxx&VAL2=yyy'">

My question is: is there anything obviuosly wrong with the first method, or is this something quirky as to how Netscape deals with 'open'

Thanks for any insight. Cheers, Neil