I almost have my first build together was wondering if I could install a piezo pickup and a hardtail bridge
"No Rules" ~ Shane Speal
You should be able to no matter what. How were you thinking? What kind of piezo (disk or rod)?
If going inside the box (and not between the box and the bridge) I would take a look at Justin Johnson's YouTube Video on disk piezos. If I can find the link I will post it, but if you search for something a long the lines of "the best piezo pickup" on YouTube... it should be within the top 5 results.
It will definitely work ok Anne, the only minor issue being that piezo's generally are used as an accoustic enhancer, and the hard tail will reduce the accoustic properties a little, having said that, it is just a generalisation, and many have done exactly as you are and achieved great results