Submitting your PR4 site to other sites which has lower PRs than yours will not affect your rankings in a negative way, as long as you do not join link farms you'll be okay. But this strategy is more of a waste of time, you should look for high
PR sites where you can receive more
PR juice.
If you need more info about
PR, read it here:
http://www.webworkshop.net/pagerank.html