SH2 runs north of wellington - basically there's one motorway out of wellington heading North, and it splits into 2 - SH1 and SH2 and each road goes either side of a big 'hill' I suppose! SH1 towards the Hutt Valley, and SH2 up towards the Kapiti coast. The first few exits off of SH2 are Kandallah, Newlands, Johnsonville, Grenada, Tawa, Porirua (don't live there tho - not too nice!) and by then you'd probably be travelling about 1/2 hour in rush hour so don't go any further!
The good side of living off SH2 instead of the SH1, is that you can get to these areas by going through the town too, so if the motorway is busy for whatever reason, you can still get home by going the 'back way' across town - something you can't do to the Hutt Valley.
Jod