I thought it was just part of my TimeMachine problems, but I've now replicated it without external drives attached and with TimeMachine off!  My poor little 10.5.1 Mac likes to get stuck while emptying the trash!  Unable to duplicate the issue with the Intel Macs in the office (mine is PowerPC).  It was making me think more and more that my machine developed a hardware issue, but I've now seen reports from other people about the exact same problem!  Hope that one gets fixed in 10.5.2.  Force Quit sometimes works.  Sometimes I have to do a hard shutdown (hold the power button down until it turns off)...