In your treeview properties window set the imageList property to the imagelist on the form. This will set the ImageIndex property to 0 by default. This causes all the nodes to have the image at index 0 in the imagelist. Set the ImageIndex property to the desired image if you do not want 0 to be the default one.
Now to have different images for different nodes you set it in code
VB Code:
TreeView1.Nodes(0).ImageIndex = 1
Here I am doing it all in code.
VB Code:
TreeView1.ImageList = imagelist1
Dim n As New TreeNode
n.Text = "Hello"
n.ImageIndex = 1
TreeView1.Nodes.Add(n)
Even done this way the image at index 0 in the imagelist is the default for all nodes initially.