If you have successfully created a new partition, then you should be able to install Win7 onto it, and it should automatically create a boot menu, to allow you to boot into either ME, or Win7.
Having said that, if your machine is capable of running ME, (i.e. you can get drivers for all the devices and peripherals) then it's almost certainly NOT capable of running WIn7. I don't know of any manufacturer who provides drivers ranging from ME to Win7.
It may well be that you can't get Win7 drivers for your scanner (have you checked the manufacturer's web site?). But as VHG says, in the (only slightly) longer term, you are going to find exactly the reverse is true - i.e. any new devices you buy will not run with ME.