I have an interactive DVD that came with one of my college course books. I need to use this for some homework. When I try to open its says I can't run start projector because PowerPC applications are no longer supported. I have Lion Version 7.1. What can I do? Can I download anything that will allow this to work?
You will need to use a computer with 10.6 (snow leopard) or earlier if you want to run that software on a Mac. Maybe a friend has an older computer you can borrow. Or maybe it will work on a computer lab machine.
1) Try running it on a Windows PC (I'm guessing backwards compatibility will be better)
2) Virtual Machine. It looks like Snow Leopard on Virtual Box is very difficult (and I'm guessing illegal) but maybe you can get your hands on a copy of Windows that will work.
If your Mac supports Snow Leopard, and you have or can get an install disc for it, you could install SL on an external hard disk and boot from that when you need to run this DVD - restart, wait for the startup sound then hold down the Option key to choose which volume to start up from. That way you don't need to mess about with your current Lion install. If your Mac came with Lion when it was new it probably won't run SL but you can check at everymac.com
If you have or can get an install disc for a version of Windows that the DVD supports then you could install that in a virtual machine e.g. Virtualbox.
As a last resort you can pick up an actual PowerPC Mac pretty cheap on eBay, and resell it for a similar price once you're done. If the DVD specifies any system requirements, edit those into your question and people can suggest suitable models.