The simplest way to get RSE is via the Update Manager: From your running instance of Eclipse 3.3, choose Help > Software Updates > Find and Install.... Choose "Search for New Features to Install", and select the "add a new Remote Site named "RSE" and pointing to http://download.eclipse.org/dsdp/tm/updates/2.0/. Select the RSE SDK feature, and perform the update process as usual.
If you prefer manual installation, you can download RSE SDK from the DSDP Target Management Download Site and extract it into your installation of Eclipse 3.3 or later, or link it as product extension.
Start Eclipse Workbench, and choose Window > Open Perspective > Other > Remote System Explorer.