I want to convert polygons into points using QGIS.
I know how it's done in ArcGIS Desktop.
If you want to decide on your own point spacing, you can use the Sextante Toolbox with SAGA functionality activated (you'll need to install saga - www.saga-gis.org/ - and specify the installation path in sextante). Use the 'polygons to line' geoalgoritm followed by the 'line to points' one. You can create a model in sextante that combines these into one step as well.
Note: you have to make sure you install the right version of SAGA - I think its 2.0.8