There should be an orange or yellow slip of paper in the box if it's the original mapping that came with the unit. If the previous owner had the unit registered with Garmin (via a
myGarmin account) then they need to de-register the device with them, you can then take it over. The unlock codes should be on there. If they never registered the unit it might be worth trying to register yourself. I did this with a 2nd hand Quest many years ago and found that the previous owner hadn't bothered, as a result I got a free update to current mapping. Garmin operate a different policy to these free updates these days (within 60 days of first satellite fix) and given that your mapping isn't supported any longer you'll be out of luck on that front. If the unit is still on their database and it's not been previously registered you might be able to obtain the original unlock codes though.
v7 mapping is pretty ancient (2004/2005) though most of the roads will still be in the same place

On new sections of road you'll find yourself driving across, what appears on the screen, to be open fields and the route that the GPS had decided upon will be recalculated when you hit a recognised road.
The last update for the non NT mapping was City Navigator 2009 though you would have to find dodgy means to get this working on your GPS once you've tracked down a copy. However, the 2008 version saw a big jump in mapping tile size which is bad news for Garmins with relatively limited memory capacity such as the SPIII and Quest. If you can track down a copy of
Metroguide Europe v9 (the last version I believe) and also get a copy of
GeoDude's MetroGold (not sure if it works with current versions of Mapsource though) you can use the mapping on your GPS (not Garmin's intention). This has the smaller tile sizes that will be of distinct advantage for your GPS.
It's quite a technical and lengthy subject but tackling it will enhance your understanding. If it's all a bit daunting then it might be best to put the SPII onto eBay and get a more recent GPS though.