Wow...I can't believe it!!
I would've never expected a Sims 2. It's a brilliant idea that Maxis has come up with. It looks SO fun. I really only found out about it like a day ago but I've been researching it a lot. The screenshots look awesome (find them at TheSims2.com). I've seen a lot of other sims fans asking Maxis to make an expansion pack about growing up and living the stages of infant, toddler, kid, adult, and grandparent. This makes the game based on reality and really just tells you that you have a limited amount of time to achieve your goals and it teaches you about how you can ruin it. The sims are also more aware of their surroundings. If two sims are making love and another enters the room, they'll have a reaction. The new create a sim feature looks cool as well. We get to personalize our sims much more.
If you have the Sims Makin Magic expansion pack, there's a Sims 2 preview disk in the case. I suggest you watch it, it has a lot of info about the game.

The Sims 2
Many of the people around me know I'm just as obsessed as one could be with the Sims. I loved building beautiful houses, making families, and watching them grow. The Sims 2 has everything that was missing from the Sims: genetics, aging, and much more. With more customization possibilities than ever - you can customize everything about your sim: eye color, hair color, eye shape etc. and their furniture: fabrics, stains etc. - no two people's games will be alike, let alone two sim creations. With 6 life stages: baby, toddler, child, teen, adult, and elder, you can watch your sims grow up, have babies (yes, the conventional method, not just by kissing!) and pass on their genes, and finally die. You can create an attic, a third floor, foundations and decks! Windows and doors can go on diagonal walls!
With the camera man mode, you can zoom feet overhead or mere inches from the ground to capture every perspective of your sims.
The Sims 2 will be the best game ever!

Specs
I checked my computer which is about two years old and it's more than capable of handling the game. Like, I have "P4", and 40 GB of hard drive, (I'm a pack rat). And a more advanced video card than they suggest. I have 256 MB RAM but I may increase that anyway, rather be safe...

This is straight from the website: http://thesims2.ea.com/about_system_specs.php

The Sims™ 2 Minimum System Specs

If you have a T&L; capable video card with at least 32 MB of video RAM (such as nvidia GeForce 2 or better or ATI Radeon 7000 or better) then you need at least:
600 MHz P3 processor
256 MB RAM if Windows XP, Windows ME, Windows 98 or Windows 2000
At least 3.5 GB of hard drive space
If you have a non-T&L; capable video card (such as TNT2 or Intel Integrated for example) then you need at least:
1.5 GHz processor
256 MB RAM if Windows XP, Windows ME, Windows 98, or Windows 2000
At least 3.5 GB of hard drive space
Recommended video cards (and the more video memory the better):
ATI Radeon 9800 Pro
Nvidia Geforce 4 or FX series cards

From the nVidia website's glossary
Transform & Lighting (T&L;) definition: Two separate engines on the GPU (Graphics Processing Unit) that provide for a powerful, balanced PC platform and enable extremely high polygon count scenes. Transform performance determines how complex objects can be and how many can appear in a scene without sacrificing frame rate. Lighting techniques add to a scene's realism by changing the appearance of objects based on light sources.

Some other notes about video cards:
T&L; video cards started shipping around 3 years ago, so if you got your computer in the last couple of years you should check and see if you have a T&L; card.

It's always a good idea to make sure you have the most current drivers for your video cards. The manufacturers usually have the video drivers on their sites for you to download. Visit the nVidia site or the ATI for the latest drivers for those video cards.