What MS Windows version do you have? In Windows XP, it would not show the ".ztd" if ".ztd" is already associated with some program.
You will not perceive any speed difference when you combine ztd files over not combining them. Zoo Tycoon will take just as long to use 100 files with 1 thing in them as it does to use 1 file with 100 things in it. (Technically, combining files uses less memory and will cause Zoo Tycoon to run faster, but not enough for you to notice the difference.) Of course, Zoo Tycoon takes longer to use 100 things (no matter how many files they are in) than it does to use 1 thing. But that is another advantage to combining files because they will be easier to move in and out of Zoo Tycoon's folders.
I tested the following step by step procedures on Windows XP. Other versions of MS Windows should be similar, but there will be differences. If you have a different version of MS Windows and cannot figure out how to do the following things, please ask. I'm sure we can figure things out as a group.
Changing Windows XP to show ".zip" and ".ztd" in "My Computer"
1) Click Start.
2) Click Control Panel.
3) Double click Folder Options. If you do not see "Folder Options", but see "Appearance and Themes", click "Apprearance and Themes" first. Then you should see "Folder Options".
4) Click View.
5) Make sure that no checkmark is in the "Hide extensions for known file types" box. If there is, click in the box to make the checkmark go away and click OK.
Associating "ztd" files with the built-in compression program in Windows XP
1) Click Start.
2) Click Control Panel.
3) Double click Folder Options. If you do not see "Folder Options", but see "Appearance and Themes", click "Apprearance and Themes" first. Then you should see "Folder Options".
4) Click File Types.
5) See if ZTD is in the list. If it is, then ZTD is already associated with some program. On the machine I was using, ZTD was not associated with some program. Therefore, I associated ZTD with the built-in compression program by doing the following:
- 5a) Click New.
- 5b) Click in the "File Extension" box and enter ZTD
- 5c) Click "Advanced>>".
- 5d) Click the down arrow next to the "Associated File Type" box.
- 5e) Look for and click "Compressed (zipped) Folder".
- 5f) Click OK in the "Create New Extension" window.
- 5g) Click OK in the "Folder Options" window.
Combining ztd files in Windows XP
1) Perform the previous two procedures if they have not been done yet.
2) Click Start.
3) Click My Computer.
4) Go to where the "ztd" files are in Zoo Tycoon. (Usually this is C:\Program Files\Microsoft Games\Zoo Tycoon\Updates)
5) Hold down the "Ctrl" key and click each "ztd" file that you want to combine.
6) Click "Move the selected items".
7) If there is no "Saved ZTD files" folder, create one:
- 7a) Click "My Documents".
- 7b) Click "Make New Folder".
- 7c) Type "Saved ZTD files".

Click "Saved ZTD files".
9) Click Move.
10) Close the My Computer window.
11) Click Start.
12) Click My Documents.
13) Click Saved ZTD files.
14) For each ztd file you want to combine:
- 14a) With the "right" mouse button, click on the file.
- 14b) Click "Extract all".
- 14c) In the Extraction Wizard, click Next.
- 14d) Hit the "End" key and and change the last 2 folders ("\Saved ZTD files\...") to "...\combined".
- 14e) Click Next.
- 14f) Except for the last file to combine, remove the checkmark by clicking in the "Show extracted files" box.
- 14g) Click Finish.
15) After doing the above for all files, there should now be a window showing what is in the folder called "combined". Highlight everything shown. (One way to do this is to hold down the "Ctrl" key and click on each thing shown.)
16) With the "right" mouse button, click on one of the files.
17) Move the mouse over "Send To".
18) Click "Compressed (zipped) Folder".
19) With the "right" mouse button, click on the "zip" file that was just created.
20) Click Rename.
21) Change the name to a name ending in ".ztd". I use one of the following names: foliage.ztd, foliage_as_rocks.ztd, nonliving_user_animals.ztd, nonspecial_animals.ztd, rocks.ztd, scenery_as_rocks.ztd, structures.ztd, user_fences.ztd, user_paths.ztd, zoo_scenery.ztd.
22) Hit the "Enter" key. When the "If you change name extension..." question appears, click Yes.
23) Click "Move this file".
24) Move the file to the Zoo Tycoon folder where the original "ztd" files were.
25) In the window showing the contents of the "combined" folder, click the "Home with an up arrow" picture.
26) With the "right" mouse button, click on the "combined" folder.
27) Click "Delete".
28) In the confirmation box, click Yes.
29) Open "Recycled Bin".
30) With the "right" mouse button, click on the "combined" folder.
31) Click "Delete".
32) Click "Yes" to confirm the deletion from the Recycled Bin.