A) Flash with the Nokia update wizard and select OS2007

B)You can download the latest OS2007 from here
Search for the OS&SDK over your right on that page.
You should enter your wlan address in order to be able to download the files.
This way you can save the OS images you want just in case the download from the wizard becames unavailable..
Once downloaded, you should rename the files as .bin
Regarding the OS2008, I would suggest give it a try...In my opinion, overall is better than OS2007
Ah, remember when you do the process to upgrade thru the Nokia wizard, select "change" (I'm not sure, but think the button is "change" or something like that) and look for the file you have downloaded.
Hope this help!