It sounds like you wrote over your windows mbr. From what I understand, its best to have the windows boot loader load up grub and then have grub let you get to Ubuntu.
First of all... I would make a backup of your system so you can always restore back to where you are right now. Some free backup tools:
- macrium reflect
I would then try a fixmbr from microsofts recovery consol as described here.
Once you have windows booting up properly, you have a few options options.
- You can avoid a lot of pain by using wubi to install ubuntu
- You can try to install Ubuntu again from a CD and see if there is an option to keep the windows boot loader.
This site has a lot of information. You might want to take a look here.