Do you have an Ant build.xml file? If so, in the New Project dialog select the "Java Project from Existing Ant Buildfile" option.
To manually load an existing project, this is what I do:
1) Create a new project, using the appropriate project kind (perhaps a Dynamic Web Project in your case)
2) Using OS tools (cp, Explorer, a file manager, etc.), copy the existing files into the new project's directory. You can do this a a single copy which retains your original directory structure, or you can be more selective and copy directories of files to new locations. For example, I often rearrange the directory structures of old projects to more closely align with the basic Maven directory structure.
3) Back in Eclipse, select the project and hit F5 - that will refresh the project and the files now show up.
4) Do any necessary cleanup such as identifying the Java source directories.