'Start / Control Panel / Default Programs'
'Associate a file type or protocol with a program'
Now you need to see which associations you want to change to another program. Unless someone has a reliable program or method for batch association changes, you'll have to change them one by one. To help you out a little, here are some of my associations (key file types in bold):
MS Word - .doc .dochtml .docm .docx .dot .dothtml .dotm .dotx .odt .rtf .wbk .wiz
MS Excel - .csv .dqy .iqy .odc .ods .slk .xla .xlam .xlk .xll .xls .xlsb .xlshtml .xlsx .xlt .xlthtml .xltm .xltx .xlw
MS Outlook (the program that comes with MS Office retail) - .hol .ibc .ics .msg .oft .vcf .vcs
MS Powerpoint...