Yes. You should reinforce the edges of the envelope with clear plastic tape (packing tape is fine, scotch tape is not wide enough) to help keep it from being ripped in transit.
Most importantly, you need to mark it clearly with MEDIA MAIL on the envelope.
Check: http://pe.usps.gov/text/dmm300/170_cover.htm for more specifics on eligibility & rates for Media Mail.
I use Media Mail often to send & receive books through www.paperbackswap.com and it generally arrives quickly and with little or no damage.
Good luck!