Landscape and portrait settings are set via the printers own preferences usually. The way the picture data is aligned can be effected by the software setting to landscape or portrait also.
Different software will use different methods of arranging the data prior to printing , or some will be using only the printers own preferences to set it.
The answer here is: After you have brought up the systems own Picture Print function hit the Small OPTIONS link in the bottom right hand corner, Select the PRINTER PROPERTIES link and to adjust the printer itself.
You also might want to go to Control Panel\All Control Panel Items\Devices and Printers and right click on the printer , bring up the printer preferences, and set it there more permanently.
It does seem like Windows 7 Version of this , defaults to landscape. I guess under the idea that it would be Pictures not text. It does not seem to be working as well as the XP version did. I was able to switch it up though.
Added Tip: I Use both landscape and portrait on may different printers (for work and play). What I like to do is create a second "printer" (or icon) in the system, with completely different settings and rename it. I do that by adding another printer, The SAME one, and telling the system to use the Same drivers (otherwise it will pile on another full set of drivers). Then I rename them using the Printer Properties. Then I go to the printer preferences (or default in XP) and adjust each for different uses.
Using that method each of the printers has a Landscape Printer and a Portrait Printer. When going to print Instead of adjusting the print preferences, I just select the appropriate printer for the job.
All of that takes a bit of careful installing, proper settings, and some testing.