Hi Silverlamp,
Here's a previous reply to a similar subject:
http://www.rootschat.com/forum/index.php/topic,304562.msg1862175.html#msg1862175To that, I would add "make sure the ceiling of your oven is very clean so that nothing drops off it onto your print!"
The whole photo will not fit in the oven once unrolled, but you should be able to get it humidified enough so that when you remove it it will lie down most of the way by itself. You can then place it under some even weight to dry and flatten out completely.
How old is the photograph? You will need to get very good professional advice about framing it, as all photographs are very much subject to damage by light, humidity and bad framing. Personally, I would consider having a copy made, and framing that, while storing the original (once flat) in an archival folder/box.
Hope that helps - feel free to ask more questions!
Cheers
Prue