Vista - limited user accounts unable to access internet

The administrator account in vista home can access the internet without
problem, but the familys standard user accounts cannot even open the program,
let alone have restricted access. When the isp's software is started, windows
trys opening the icon as an image file, not as an application. this is true
for all user accounts except administrators. Parental controls have not yet
been set, IE 7 works fine in admin account and McAfee seems to be set up
ok????? ISP have said this is a windows issue they have come acrss before,
but have no idea how to resolve it.