matplotlib error with tkagg

[Federico]

Hi, I'm using python 2.2 under windows...when I use the 'Agg ' backend it
works fine but when I try to use the 'TkAgg' one I've an error message that
says :
....
....
"import tkagg                 # Paint image to Tk photo blitter extension
  File "D:\PYTHON~1.3\Lib\site-packages\matplotlib\backends\tkagg.py", line
1, in ?
    import _tkagg
ImportError: DLL load failed: " impossible to find the specified procedure

What do I need? with windows installers Agg and TkAgg should work without
install any requirements or not?
Thanks