i had installed windows 7 in my MAC os X 10.6.8 using bootcamp. Now i want to upgrade to MAC os X yosemite. i want to know whether it will affect the windows7 which i had installed already or anyother software installed in my current os.
if so whether i have to take any back up of the mac and do it.
suggest me to upgrade to the current version of MAC os X yosemite
You should always have a backup before upgrading, if nothing more than for a way back if you don't like it.
You should also backup your Windows partition using whatever tool is available for that.
It is entirely possible it might damage your Bootcamp partition.
For other software compatibility, see here: http://roaringapps.com/apps
For your Printer/Scanner, see here: OS X: Printer and scanner software available for download - Apple Support
Any PowerPC-based apps will also not work in anything after Snow Leopard.
You can see what are PowerPC only by opening System Profiler (hold Option and select it from Apple Menu).
Go to Software>Applications and sort the resulting list by Kind. Anything that is listed as PowerPC will not work. There is no way to make it work besides upgrading it to a version written for an Intel processor.
Upgrading from mac osx 10.6.8 to mac os x yosemite
