Question about enlarging digital photographs. [View all]

So... I have a couple photos I want to enlarge. Really enlarge. To 30" x 40". Trying to figure out pixels per square inch is making me crazy. Online sources are both helpful and confusing. For instance, one says you can't use photoshop to enlarge pictures but you can use it to downscale photos. It also says 72 ppi will be pixelated if blown up. What I've shot comes up as 72 ppi with an image size of 48" x 32".

My questions are:

If I downsize the image to 30x40 at 72ppi, will it be all pixelated?
or
Can I change the the ppi to 300 and then downsize it to 30x40? Will that be pixelated, too?
and
If both of these lead to gross pixelation, what's a gal to do that wants her own images up in her living room?

I'm using Photoshop Elements, if that has anything to do with anything.

This whole question makes me flash back to doing word problems in math. Please help!!