Go for PC2100 DDR. Unless you plan to upgrade your motherboard in the near future, PC2700 at best would run as fast as PC2100, and at worst wouldn't run at all if the motherboard isn't compatible (for whatever reason).

For future needs, <a href="http://h20015.www2.hp.com/en/taskPageSelect.jhtml?reg=&plc=&lc=en&cc=us&prodId=hppavilion90862&pagetype=prodinfo&docparent=prodin fo">here</a> is the HP page about your model.