You can import your WAR file in WSAD.
Goto File -> Import, this will start a wizard to import the WAR file. Specify the location for your war file and the project name.Follow the steps. Once finished you can see your web project in the Project Navigator window of the j2ee perspective.
WSAD provides you with a WAS test enviornment where you can deploy your war file.You need to create the new test enviornment. Go to the server perspective. Right click and say "New server and server configuration".Give a suitable name for your server and select the server type viz. Websphere version 5.1, websphere version 5.0 or whatever is appropriate.
After this, you could see your server name in the server configuration window.Double click this, this will open a window where in you can configure the server, viz Ports,Datasource,Enviornments,classpath,etc.
Once this is done save and close this window.
Next go to the server perspective, right click the server you created, where in you see the option "Add and Remove project" . Add your web project from the available projects to the configured projects.
You are done and now you can start the test enviornment server to run your application.
Hope this helps you !!!