why to install linux after installing windows in dual boot

The problem might lie with the way the format of the harddrive being used. For windows to work it needs to first clean off and then setup the drive. Setup off the cdrom should do give you this option. Dual boot might work well on a separate drive? What worked for me was I first installed windows on a clean drive then linux on the same hard drive. Linux setup gave the option to install with windows on. At each boot the screen gave the option of either windows or linux.

There are possibly several reasons for this, but a major problem is the formatting. Linux uses such formats as ext3 and ReiserFs, whereas Windows uses NTFS on current versions and FAT32 for older operating systems. Linux is quite happy reading FAT32 or NTFS, and you can navigate to the Windows partition and open files. However, Windows will not read any partition formatted for Linux and is thus unaware of it's presence. This means that a Linux setup will take the Windows partition into consideration and offer the option of overwriting or running in harmony. If it runs in harmony then the bootloader GRUB will supply the option of choosing which operating system to boot. Since Windows cannot see the Linux partition it will read the hard drive as smaller and install it's own boot files in the MBR, thus providing no option for boot selection. I suspect that both operating systems will exist, but GRUB will no longer be accessible and thus Linux will not boot.