Download the map. It should be a .bsp file. If it isn't you need 7zip.
Once you have 7zip, rightclick the .bsp map file, and click add to archive. On the left 1 or 2 rows down you should see a file type option, click the drop down menu and choose .bzip or something, you should see the file name at the top become something like _____.bsp.bz2
Put the .bsp map file in the maps folder ip/tf/maps and then if you have a redirect (i think most done for fast dl) you put the .bz2 file in there (ip/tf/maps).