I remember when I played HCE all the time as a kid-- there's no way I could deny helping someone get into it!
The link I'll provide will actually take you to a site where you can get a ton of custom maps from; I used it all the time back in the day. So, the link you're looking for is also a great place to kick off some custom content.
If you'd like a little more research, a great reference is the Halo wiki.
If these can't help, the only other place I can think to point to is http://halo-fixes.findforum.net/t47-how-to-update-to-1-10