Can I install Garmins City Navigator NT 2008 on my new 78s.
Sure, why not? However, you do realize that it's copy protected, right? If you have the DVD version, it will become permanently locked to the first unit it's installed on. So if it was already installed on another GPS, you won't be able to put it on your 78s.
I could be wrong, but I think 2008 can be unlocked to two GPSs. I think 2009 was the fist version to only allow you to unlock to one GPS. I think it is a rip off how they tie the software to a particular GPS. I can understand only allowing it on one GPS at a time, but not allowing you to move it from your old GPS to your new one. However, I like the update feature where for about $60 you can get free updates 4 times a year.
That's interesting. Certainly worth a try, but I thought the multiple install option went away some time ago. If you're concerned about using City Navigator on more than one unit, you can buy the preloaded data card version. It can be used in any GPS, but cannot be duplicated. It can also be used on your computer in Basecamp, with the card in a USB reader.
However, it is highly advisable that no additional data be added to a Garmin prerecorded data card. Thus you would not be able to add any overlay/transparent mapset, like contours, etc. to the card with CN. You will have some free space on the 78s internal memory, but this will not be as large nor as flexible as having CN on DVD.