I'm not 100% sure of gmail to outlook mapping, i assume it would be the same as any other pop server... using other servers I have been able to use the "backup" feature and preserve the folder structure.
I've transferred accounts successfully (including folder structure) by copying the user data and application data from OS to new OS, but I'm unsure how this would work upgrading Outlook. There are some differences in the structure of these between XP and 7 too, and you would need to do a little research.
Having a 2nd machine on hand to test your transfer method would be beneficial, so when you do it for real you will have worked out any bugs. If you can find or borrow one for a day...
Edited by TsVk!, 21 March 2014 - 02:24 AM.