We bought Sims3 for PC but now someone tell me that we must have bought the Sims and Sims2 then it can be install on the PC. Is that true and if so where can we get install disk to go on.

Hi. Welcome to Fixya!
You don't need to install Sims 1 and Sims 2 to be able to install Sims 3 to your computer. For the expansion packs and stuff packs for Sims 3 you need to install first Sims 3 base game for it to work on your computer. However your computer must have the system requirements of Sims 3 to be able to run it properly. Here is the system requirements for Sims 3 :
FOR WINDOWS XP

* Windows XP (Service Pack 2)
* 2.0 GHz P4 processor or equivalent
* 1 GB RAM
* At least 6.5 GB of hard drive space with at least 1 GB additional space for custom content
* 128 MB Video Card with support for Pixel Shader 2.0

FOR WINDOWS VISTA
* Windows Vista (Service Pack 1)
* 2.4 GHz P4 processor or equivalent
* 1.5 GB RAM
* At least 6.5 GB of hard drive space with at least 1 GB additional space for custom content
* 128 MB Video Card with support for Pixel Shader 2.0

For computers using built-in graphics chipsets, the game requires at least:
* Intel Integrated Chipset, GMA X3000 or above.
* 2.6 GHz Pentium D CPU, or 1.8 GHz Core 2 Duo, or equivalent
* 0.5 GB additional RAM

SUPPORTED VIDEO CARDS
NVIDIA GeForce series
FX 5900, FX 5950
6200, 6500, 6600, 6800,
7200, 7300, 7600, 7800, 7900, 7950
8400, 8500, 8600, 8800
9600, 9800, GTX 260, GTX 280

ATI Radeon™ series
9500, 9600, 9800
X300, X600, X700, X800, X850
X1300, X1600, X1800, X1900, X1950
2400, 2600, 2900
3450, 3650, 3850, 3870,
4850, 4870
Intel® Extreme Graphics
GMA X3x00 series