Yes, you can change the font name, size, and bold attributes. Assuming a treeview on a form:

thisform.Treeview1.Font.Name = lcFontName
thisform.Treeview1.Font.Size = lnFontSize
thisform.Treeview1.Nodes.Item(lnItem).Bold = .T.

where lcFontName is the the name of the font, lnFontSize is the font size (interestingly it is seen in the debugger as a currency type), and lnItem is the node number or the nodekey. I don't believe that you can set to italic or underline.

You can also change the background and foreground colors of the nodes.