4 weeks and 2 Questions - Vanuatu and the Solomon Islands

Ok, I've now narrowed it down to Vanuatu and the Solomon Islands!

2 questions...

1.) Weather - I'm traveling from Nov 15 to Dec 15, will Vanuatu be too wet, just go to the Solomons?

2.) Keep it simple - I am very active and adventurous, but want to force myself to not be too active on this trip (i.e. traveling around, dealing with logistics hell the whole time)...but still want to be pretty darn active ;) looking for beach time, dive time, trekking/village time, option for some nightlife...should I focus just on Vanuatu?...or should I do 2 weeks in Vanuatu and 2 weeks in the Solomons?

Please let me know what you think, any other useful info much appreciated!

Basically, that is the beginning of the wet season. However, it is the best weather in some parts of some islands, notably the Lau Lagoon in Malaita. There are lots of islands and lots of microclimates. Mostly the weather is fine for some of ever day, and often wet in the afternoons.
For Solomon Ilands, I recommend the Western Province for beaches and chilling, Malaita for villages and trekking.
However, your major problem in both countries will be that that is the time when the locals are returning home from school, college and work for Christmas and the summer holiday. Ships, local rest houses and villages will be full, so it is wise to book both travel and accommodation in advance.

Thanks OzGirraffe.

I'll be starting with a few days in Sydney before heading to the islands, do you happen to know of a good agency I could book my travel through?

I've read the LP for some suggestions, but curious if you know of a specific agency that's good, thanks!

Basically, you can book flights on the airline sites (Solomon Airlines and pacific Blue (Virgin)). Other internal travel has to be booked locally. Accommodation links are on the Visit Solomons website.
The only travel agent I have ever used is the local independent Casino Travel in Northern NSW. If ou contact them, ask for Claire.