The registry values if any along with any files inside a folder being created at the time have to be removed. The add/remove programs or now seen in Vista Programs+Features won't be able to do much since the installation was halted before finishing. Generally a good working installer may simply overwrite or remove it before proceeding if this was a download you could save to the drive first and not simply run the installer.
One old registry program that will list the newest programs installed in the main window is the RegCleaner freeware seen at Regcleaner
I usually recommend that for the advanced user since the automatic registry cleanup tool is an option found on the menu bar namely tools>registry cleanup with a side menu that comes out when selected for further options. In the main window that displays all non MS programs installed where you would simply place a check next to the newest item at the top with the word new seen on the right side of the item and click the remove button.
The warning for this is to first verify the item before proceeding since that could end up being a completely different program if no main registry key had been made. That's why that one is for advanced users since reg mods are a bit risky at times. A folder on the drive in the Program Files directory also has to be verified first and simply not another item currently installed before seeing that manually removed.