After you upload the file it goes to the download page for that file. Then you give the link to people, like so:
The problem is that in 2.49b the file opens in Shaded mode and in 2.5 Shaded mode doesn’t exist so it opens it in Solid mode which neither in 2.49b nor 2.5 shows the spotlight. Note that when you press P the spotlight shows up. I don’t see a way to get the spotlight to show up in the 3D view unless you can use the GLSL setting instead of Multitexture in Textured mode.