G'day Derekc75,
Unfortunately, it isn't quite as easy as cascaderailroad makes it out.  Firstly, you need to unzip the folder texture.zip (Trainz will not do so automatically for you), which means that will need somewher to store the 70 odd folders that this creates.  My recommendation would be to extract the file to your &trainz%/Userdata/Local folder, where, after extraction, you will find a number of new folders named "Hog00", "Hog01" up to "Hog71", each of which must then be INDIVIDUALLY imported (File>Import Content...) in the manner expressed above by cascaderailroad, as per any other normal content...
...on the other hand, you could download the texture files from the following link..
http://www.storage.victrainz.com.au/Jerkers_DEM_maps/HOG_Texture_Set.cdp
...where simply installing the downloaded file as a single file (after it has been downloaded), will install ALL of the individual files in one fell swoop...
...in this case, using the File>Import cdp option from the file menu
...the odd thing about all of this is that none of the above should be necessary.  The HOG texture files are ALL "BUILT-IN" content for TRS 2009 onwards (you can check this before you do anything else) but for reasons I have been unable to ascertain to this day, they seem not to be known to CM and therefore do not 'work', until CM is 'forced' to recognise their presence (which re-installing them does, inexplicably defeaings the whole purpose of having them built-in, in the first place)...
Jerker {

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