I am not very knowledgable on TFS, but assuming you are using a TFS plug-in for Eclipse, it seems that editing a file should check it out automatically. I found a couple of references that seem to indicate so, but you may be able to find other references or specific issues through a web search.
http://msdn.microsoft.com/en-us/library/jj155783.aspx
http://msdn.microsoft.com/en-us/library/gg490745(v=vs.100).aspx