The very first and oldest Plants vs. Zombies game, if you can find that one, should play:
Plants vs. Zombies 1
MINIMUM PC REQUIREMENTS
Windows 2000/XP/Vista
1.2GHz X86 Processor
512MB RAM
65MB Hard Disk Space
DirectX 8.0
128MB Video Card
DirectX Compatible Sound Card
CD-ROM Drive
The original Garden Warfare requirements offer no support for any of Intel's junk:
Plants vs. Zombies Garden Warfare 1
Minimum:
Required: Internet connection required to install and play
DVD-ROM: N/A
OS: Windows 7/8 64bit
Processor: Intel Core 2 Duo @ 3.0 GHz
RAM: At least 4GB RAM
Video Card: NVIDIA 8800GT, AMD/ATI Radeon HD 5750
Sound Card: DirectX 9.0c
DirectX: 10.0+
Hard Drive: 15 GB
Input: Keyboard, Mouse or Dual Analog Gamepad
There was a second pre-GW game, however, since it was for Android, I never copied its requirements to my database. Here's a comment I found about it:
there is no system requirement needed for running Plants vs Zombies 2 but the Android Emulator which you need for running Plants vs Zombies 2 on your PC or Laptop or Mac requires the following system requirements.
- O.S: Windows XP, Vista, 7, 8 or OS X V10.7 or V10.6
- Ram: Minimum 1 GB, Recommended 2 GB
- Processor: For Window: 2.33GHz or Intel® Atom 1.6GHz and for Mac, Intel Core Duo 1.33 GHz
That was from here: http://www.fasttechtips.com/plants-vs-zombies-2-for-pc-laptop/