Here is what I did:

1) I downloaded them from halomaps
2) Unzipped it
3) Placed the files in the maps folder
4) Put the names of them in the maplist.txt file

And they still won't work

Any help would be greatly apreciated

Create a folder called "extras" (or anything for that matter) in the maps folder:
C:\Program Files\Valve\Steam\SteamApps\[Steam Name]\portal\portal\maps

Note: [Steam Name] is your Steam user name.

Then extract the content of the zip files to that folder. You can then access the maps through the Bonus maps menu.

Thanks Dennis I needed that