For some reason the Marketplace is not bundled in the Eclipse Classic distribution. However it is easy to install. I'm showing this for Eclipse 3.7 (Indigo).
- Open Help - Install new Software…
- Select the update site for the current Eclipse version (usually it's simply named after the version and has the URL http://download.eclipse.org/releases/indigo
- Search for marketplace
- The entry Marketplace Client should appear
- Install as usual