overI installed Mint 12 KDE from DVD to Hard Disk, but it will only boot to Windows.
That is a pretty good indication that you did not:
1. Install the Mint Grub2 bootloader to the master boot record of the drive
2. Did not configure the boot file of whatever version of windows you are using to boot Mint
You probably needed to resize if you had a standard windows install so you would have room on which to install Mint but that in itself is not going to allow you to dual-boot. You haven't posted enough information for anyone to give you specific instructions.
Do You have only one physical hard drive?
Do you have both windows and Mint installed on this drive?
Do you know where you installed the Mint Grub2 bootloader?
Can you post your partition information? Easiest way to do this is to boot the Mint Dvd, go to the menu and find the Terminal and type:
That is a lower case Letter L in the command, not a number one.
Or you could boot the Mint disk and if you are able to access the internet, go to the site below, download the bootinfoscript, read the instructions in the link in the Description paragraph and then post the results.txt file here. A lot more useful information comes from this.