Create a / (root) partition, which you have already done, followed by a Swap partition, preferably 1 GB. Install Grub bootloader in the Windows MBR. Choose "Manual" partition
This can be done at the last step while installing Ubuntu where it gives a summary of where the system will be installed.etc. On the bottom right-hand side there is an "Advanced" option, click on it and make sure Grub is installed in (hd0,0) ,ie, in the first hard drive and in the 1st partition.
Now when you finish installing Ubuntu , the PC will reboot and you will be presented with Grub Boot Menu with entries for Ubuntu & Vista.
Here is an excellent tutorial for Dual boot Vista & Ubuntu
Dual Boot Vista & Ubuntu
Best of Luck