Does the sims 2 need to be installed in the PC before installing the sims 3?

You don't but the game might run more smoothly if installed in order.

The order is:

The Sims 2™

University

Nightlife

Christmas Party Pack (US) OR Holiday Party Pack (UK)

Open for Business

Family Fun Stuff

Glamour Life Stuff

Pets

Happy Holiday Stuff

Seasons

Celebration Stuff

H&M Fashion Stuff

Bon Voyage

Teen Style Stuff

FreeTime

Kitchen & Bath Interior Design Stuff

IKEA Home Stuff

Apartment Life

Mansion & Garden Stuff

Also, be sure to patch whenever you are prompted by the game to do so.