You can access your Windows *files* by doing the following:
# mount /dev/hda1 /mnt/windows
Your windows files can now be found in /mnt/windows.
You can attempt to run your Windows *programs* by installing WINE (or CEDEGA if it's a game requiring DirectX):
$ cd /mnt/windows/where_ever_your_program_is
$ wine program_name.exe
If, however, you need to run Windows (the actual OS) from inside Linux, consider using VMWare, as has just been said.
Hope this helps