I used LinuxLive USB Creator (www.linuxliveusb.com/) to create a bootable Ubuntu 13.04 USB Drive and installed alongside Windows via that method. I have a 500GB HDD and opted to split that in half, which can be easily done in the partition manager that is built into the installer. Had no issues with lost data and GRUB gives me the choice whether to boot into Ubuntu (default) or Windows.
Alternatively, you could partition the drive from within Windows & then run the Ubuntu installer. I prefer to use AOMEI Partition Assistant as it has a good GUI and (I feel) is beginner-friendly.
Unfortunately I can't find a good guide to help with the process, but the Ubuntu installer makes the whole thing very user friendly.