In some networks with Windows Vista client computers Remote Desktop can become excruciatingly slow or stop working altogether. If that happens to you, try the following command (as one line) in a command line window or as a Run... command on the Vista client computer:

netsh interface tcp set global autotuninglevel=disabled

If this doesn't solve the problem, undo the change with the following command (as one line), which reinstates the default setting:

netsh interface tcp set global autotuninglevel=normal

Technical background: Vista is the first Windows version to employ TCP auto-tuning, particularly for the RWIN (Receive Window) setting. Usually this works fine, but under certain circumstances it fails and needs to be disabled.