Irian Jaya is the Indonesian side of New Guinea. After the independance of Indonesia, Irian Jaya remained Dutch for some 15 more years.
The islands is covered with thick forests and it is very hard to get from A to B. Think of this as part of the fun and you will have a great time on Irian Jaya.
Most travelers head for the Baliem Valley via either Jayapura or biak. Baliem Valley is where the Dani people live. The main town of the valley, Wamena, has some modern facilities but even here you will see men wearing their penis gourds proudly (that’s the only way to wear them, actually) and women in grass skirts. From Wamena you can explore the rest of the valley using guides.