Yes it is true that we can format the text when we type in Gtalk chat window.Even though we dont have buttons to make a text bold or Italic,there is a easy way to do that.
To make the text bold format we have to add asterisks(*) in front and end of the word(s).
Eg : *I am in bold*
Result : I am in bold
To make the text italic format we have to add underscore(_) in front and end of the word(s).
Eg : _I am in italic_
Result : I am in italic
Combination of both bold and italic
Eg : *_I am in bold and italic_*
Result : I am in bold and italic