How to install an expansion pack on The sims 2 double deluxe?

If I install a new expansion pack for Sims 2, would it become my main disk?

• I have Sims 2 Apartment Life as my main disk on Sims 2 and I want to install Sims 2 University Life. The thing is, my sister also plays Sims 2 and she already has University as her main disk and we are afraid that if I install it, it will become my main disk, too. I want Apartment Life to stay my main disk; it was the first expansion pack I installed and so far, it has always been the main disk for my game.

• Answer:

  The newest disk release will become your main disk. University is an old one, so YOU can safely borrow it because Apartment Life will stay your main disk. Your sister can't borrow your Apartment Life, because she will need it. HOWEVER... Is that University disk actually the "University Collection with Teen Style Stuff and IKEA Stuff"? If it is, then it is newer, has an updated patch, and that might become your main disk. One thing for certain, the "Fun With Pets Collection With Mansion & Garden Stuff" will be your main disk because it was the final Sims 2 release. If you have that one, then you can borrow anything you want, and not have to worry about not having the disk.