Unable to dual boot after installing windiws 8

Sorry if this is not the right forum.

I have 2 partitions on my disk drive. I used to have vista on one and windows 7 on the other.
I reformatted my vista partition and installed windows 8 on it.
after this when my computer boots up it doesn't give me the option of which OS I want. it boots into windows 8 always.
I can see the windows 7 partition thru explorer.
how do I enable dual boot again.

thanks

i don't have that option. when i go into advanced system settings it only shows windows 8 as a boot option.
apparently i needed to choose custom install when i installed windows 8. since i chose the regular install i'm unable to get to my windows 7 system anymore.
any help is appreciated.

thanks. i'll check it out. hopefully it will solve my problem