one thing to add, you mentioned that there is no drive letter..
so right-click the primary partition in disk management and select "change drive letters and paths" then select "change" and select a drive letter.
Also i would say that Ubuntu is fine, its just that the windows boot loader does not contain the info for ubuntu to boot. So i think that the easiest way would be to download "
easyBCD 2.0 BETA" (you have to register at their site/ also get the latest build)i walk you through with this....
Also, how did you install Ubuntu, normally or through Wubi?