It's so painful to install plug-ins in MyEclipse 8.x. It tries to block you from directly access update URLs with a so-called Software Centre. Things become even worse if you're behind a proxy. What's funnier are You can't update Eclipse 3.5 behind the proxy and MyEclipse still refuses to base itself on Eclipse 3.6.
Anyway, I just want to share a tip in plug-in installing in MyEclipse 8.5. See the screenshot. Note the "Connect directly to host" option.