in inkscape how to clear all the guide lines forever with one click

The stable release of Inkscape (0.48.1) does not have a command to delete all guides at once (it's a known feature request and has just been implemented in the development branch, to be part of the next stable release 0.49).

For now, there are two options with Inkscape 0.48.1:
a) You can install an extension which does just this:
<http://screencasters.heathenx.org/blog/2009/06/09/inkscape-extension-remove-guides/>
b) You can trick 'Extensions > Render > Guides Creator…' to remove existing guides without adding new ones:
   Adjust the 'Guides Creator…' settings like this:
   - Preset: 'Custom…'
   - Vertical guide each 'None'
   - Horizontal guide each 'None'
   - Start from edges [ ]
   - Delete existing guides [x]

   … and click on 'Apply'

Thank you, but where can I find "the 'Guides Creator…' settings"?

I meant the options you can set in the dialog that opens when you apply 'Extensions > Render > Guides Creator…'

For a short description of the 'Guides Creator', see also:
<http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Extensions-Render.html#Extensions-GuidesCreator>

In Inkscape 0.91, there is a new option to delete all the guides at once. You'll find it under Edit > Delete All Guides.