PHP / HTML question

Hi boys and girls, I'm using PHP to upload a file, however, when they click the "Browse" button to look fo the file they want to send off their local machine, it either opens with *.* all files in Explorer or *.HTM files in Netscape. Is there any way, in either PHP or HTML that I can specify the following : 1. I want it to open *.jpg (as that's all I want them to upload) 2. Specify a particular opening directory. (ie. where the jpgs are likely to be stored on my particular users machines) Any help would be much appreciated. Thanks Geoff