I think there is only the one nursery in Highgate - on Church Road, which only takes children from 2+. There are also various Montessori playgroups etc which again only take children from 2+. The nearest nursery which takes babies is on Muswell Hill Road but closes at 5.15pm which is almost impossible to get back for if you have to travel.
Crouch End, loads of nurseries but don't know which are good.
It depends on whether you're asking about nurseries or nursery schools i.e. what age and what you expect from it such as term dates, education etc. There are a couple of lovely Montessori's which operate with school-type terms that take children from 2, fewer facilities for much younger children. All the infant schools operate nursery classes from the September after their 3rd birthday which you need to apply for using forms available from the schools - but they won't guarantee you place in Reception. There are also some excellent playgroups like Stationers and the 3-2-1. Best is to go round and visit them and see where you feel comfy.