Using winmerge as a merge tool in Visual Studio Team Suite

Found in msdn, to change the diff/merge tool used on conflicts with TFS:

Go to Tools > Options > Source Control > Visual Studio Team Foundation Server > Configure User Tools...

Add a Compare pointing to winmergeU.exe and using:

/e /x /s /wl /dl %6 /dr %7 %1 %2

as a command-line argument.

Repeat the operation for merge, this time using:

/e /s /x /ub /dl %6 /dr %7 %1 %2 %4

Enjoy!