Similarly insertion into a double linked list goes along the lines:
Code:
+-+--nA->+-+
|A|      |C|
+-+<-pC--+-+

Link B in:

+-+---nA--->+-+
|A|         |C|
+-+<--pC----+-+
 ^           ^
 |           |
 |    +-+-nB-+
 |    |B|
 +-pB-+-+

Now redirect the links between A and C:

+-+--nA->+-+--nB->+-+
|A|      |B|      |C|
+-+<-pB--+-+<-pC--+-+
I'll leave working out the code to you, which should be really easy with this in front of you. Also to figure out for both single and double linked lists are inserting at the head and at the end, and deleting (head,middle,end).