Re: Will installing sims 3 make my laptop run slower?

Yes.  I'm not sure how noticable a difference it would be--mostly likely very small if you're only talking about the base game and still have a lot of memory left on your hard drive, but all application/programs you add, Sims included, changes the speed of your computer because it's going to occupy space.  The less space on the hard drive, the slower it can become, especially if don't have very much RAM.  It's by no means going to kill your computer or anything but it does slow your computer down in the long run.  This applies to all computers and programs, especially memory-intensive games like the Sims.  Just keep that in mind.  🙂