Proxy problem while Connecting Salesforce from Eclipse – Force.com IDE

Error:
Save error: Unable to perform save on all files: Unable to tunnel through proxy. Proxy returns “HTTP/1.1 503 Service Unavailable”

Technical Solution:
Problem seems to be that you are under proxy and Eclipse is unable to route the requests through the proxy.
Try if one of the below works for you also,

1) Configure Eclipe Proxy Settings:
Window ->Preferences ->General ->Network Conenctions
You can set your proxy settings here.

2) Use Firewall Client for ISA Server:
http://www.microsoft.com/DownLoads/details.aspx?FamilyID=05c2c932-b15a-4990-b525-66380743da89&displaylang=en
What this does is routes all requests through the proxy.