Depending on how Netscape was configured, downloaded files may be stored in various folders, which makes them much harder to locate than if they are placed on the desktop.

The easiest way to find the files is to do a search from the Finder, which can be selected on a Macintosh by pointing to the icon at the far top right of the computer screen and holding down the mouse button. This will show a list of all applications currently loaded into memory.
Select the Finder from this list.

Now select Find... from the File menu, or press the command and F keys simultaneously (Command is the key with the little cloverleaf design alongside the space bar).

The Find File dialog box will then appear, and you can type in the name of the file you want. You don't have to type in the full name, any fragment will do.

Press the Return key, and the computer will search it's hard drive and display a list of any files matching the search string.

Double click on the name of file you want in the search dialog box, and it will automatically open, assuming you have enough RAM to load that application.

If you do not have enough memory, you may have to return to the icon in the upper right of the screen, select unnecessary applications one by one and quit out of them to get back enough RAM to load your application.

You can quit any program by pressing the command and Q keys simultaneously.