when i try download any car for my sims 3 game the download file isnt recognised and it says that windows explorer cant open the file and asks if i want to select a programme to open it with.

Click on the Help menu, then choose Sims 3, then "CC Basics" and start reading. It will give you the info you need, including links to pages specific to sims3pack or package file content (which the cars will be). Good luck!

(I'm closing this thread, though, as this area of the site is for problems with MTS, and this is very much not that. )