This is one problem which I have been trying to solve for a real long time with my Eclipse 3.5 Galileo. The problem was that I was not able to connect to the network to get the repository for the plugins. For long I have been doing the manual install of the plugins but it does not always works out. Like when I wanted GWT Designer plugin, I was unable to find the .zip file for the same.
So, the solution:
1) First go to Windows->Preferences->Update/Install sites and for one of the sites click the Test Connection tab on the right.
2)If it takes long and does not connect to the repos site, that means there is something wrong with your eclipse setting or the the test site. Here, we assume that there is something wrong with your eclipse settings and try to retify it.
3)There must be a proxy server which your company must be enabling, so u need to give proxy data with Manual mode in Windows->Preferences->General->Network. Give it for all 3, HTTP,HTTPS and SOCK.
4)Again, go to step 2 and try it. If it still does not work then in Step 3 just clear the SOCK proxy details. Because your company might not be enabling a SOCL proxy and eclipse first check for SOCK and then HTTP.
5)Again try Step 2 and it should be working.. Congrats!!!!
4)Again repeat