I went through quite a few steps, figured out how to use PortableApps to run IrfanView and other Windows standalone programs in Ubuntu. Anyone interested in the details, see http://raywoodcockslatest.blogspot.com/2010/06/ubuntu-1004-irfanview-and...
That writeup ends with a question about making a WinXP application the default program for a certain filetype when running that app in Ubuntu via Wine. I've posted a succinct statement of that question in this forum. See https://portableapps.com/node/23822