Boot managment
 

Hi,
I already had centos on one partition, after that i install window7 on another partition.When i turn on my system only windows7 goes up in boot.
how can i have both of centos and windows7 in boot?

Yes, you can, but Windows doesn't play nice with other operating systems. Their bootloader overwrites the linux bootloader, so you need to reinstall GRUB and set it up for the dual boot.

http://wiki.centos.org/TipsAndTricks/ReinstallGRUB

Basically two ways. One is to use grub to load both but it is possible to let windows boot both. Most linux people tend to use grub. Tons of web pages devoted to that since it has been a problem for decades.

Consider using virtual machines for testing too.