Traveling around South Pacific

I am just starting to look into this as i will be in australia in january and i could have between 3 or 4 weeks to spare in February so i would love to visit some south pacific islands.

how do you travel between them? boats? just flying? which ones would you visit if it's just 3 or 4 weeks in total?

If you are going between say Tonga and Samoa you fly. If you are going between the islands of Fijiit is by boat or small plane. Leaving from Australia your best options is probably Air Pacific to Fiji then you could go on to Samoa, Vanuatu or Tonga (I prefer Samoa). Pacific Blue also flys to the islands from Australia but the problem is they don't fly between them. Maybe Pacific Blue or Air Pacific to Fiji, AP to Samoa, Virgin Blue back to Australia.