You probably won't be able to change the default dialog view in XP. That's a feature upgraded in the newer versions of Windows.
People sometimes ask me what's better about Windows 7 than XP. This is one small thing.
I did read about an undocumented "trick" for XP once, but I've never seen it actually work myself and I chalked it up to lore... But hey, trying it would be easier than upgrading to a newer version of Windows, right?
Change the view to the one you like (e.g., thumbnails), then hold down the Control key and close the dialog with the X in the upper-right.
Hope it works (but I'm not holding my breath).