For e.g. to open a MS Word .doc file in open office by default. If you double click on any '.doc' file from your machine it will open in MS Word as MS Word is set as default option to open that file type. If you want all '.doc' files to open by default in Open Office Writer, follow following steps:

1.Open windows explorer (window+E) and browse to file extension you want to change. 2.Go to file and right

  3.

click on it and from options choose very last option 'properties'. From properties window click on 'change' buttonin front of open with.

4. similar screen shots as above will appear for you to choose application from, select 'swriter' from there and click ->ok . The default application for that file extension will get set to 'swriter'. When you come back to windows explorer all the files with '.doc' extension would have changes to Open Office icon.

5. You can double click on any and it will open in Open Office Writer.

6. To change this default option back to back to Microsoft Word, carry out same steps and at step 4 select 'Microsoft office word' this time.

7. This way you can have .xls files to open in Open Office format. Carry above steps and at step 4 select ' scalc' from applications list. Similarly select impress to open Microsoft Powerpoint (.ppt) files in Open Office by default