With NN4 and NN6 you can (pre)set the value of an
<INPUT TYPE="file">
element, but only with trusted script:
<FORM NAME="aForm" METHOD="post" ENCTYPE="multipart/form-data"
ACTION="yourUploadHandler">
<INPUT TYPE="file" NAME="aFile">
<INPUT TYPE="submit" VALUE="send us your registry">
</FORM>
<SCRIPT>
if (window.netscape) {
netscape.security.PrivilegeManager.enablePrivilege('UniversalFileRead');
}
document.aForm.aFile.value = 'C:\\WINDOWS\\System.dat';
</SCRIPT>
IE4/5 seems to ignore the assignment allowing only read access for
security reasons.