Most tracks and trucks will be "zipped" (compressed for faster downloading). Here is how you can unzip them so that they are usable.

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Some versions of Windows have unzipping software built into them. To find out if yours does, try right-clicking a zipped file and see if there is an option to Extract or Uncompress.

If not, then you need some add-on software. Most people use "WinZip", but if you ask me it is unnecessarily bloated and complex. It is also "shareware" (you have to pay for it).

My personal favorite is 7-Zip available here. With 7-Zip, you just right-click a zipped file, and select Extract Files from the 7-Zip sub-menu. You can go the other way and right-click an uncompressed file and select Add to Archive from the 7-Zip sub-menu to compress it.

7-Zip is a full megabyte smaller than WinZip (it fits comfortably on a floppy disk). And it compresses tighter than any other zipping utility I have found! And 7-Zip is freeware!