If you have your Harmony 880 drive an IR blaster it is very easy to interface with UPB using the PCS 6 button UPB controller with IR (table top)
Here I do not know why Automated Outlet doesn't list this. It can be purchased from Home Controls, San Diego. A little Pricy but the only thing with direct IR to UPB control. Just place the blaster and the UPB controller a few inchs apart and you have IR control of 6 "scenes". I have a Pronto 1000 with RF-IR doing this in a AV rack.
( I just read Steves Post on an IR UPB solution. Sound like there are 2 options)
I would suggest the Simply Automated products for versitility and options. If you have a Fry's near by you could pick up switches, Lamp Modules, and Appliance Modules for under $40 each. The Fry's near me still has them.
Download the FREE UPstart software
Here Once you program your devices your system does not need a computer. There is a short learning curve to program the switches. But there is a lot of experience Here on Cocoontech, so ask a lot of questions. We will get you through it.
Before jumping in with both feet I would sugges you purchase an evaluation kit with a computer interface module and at least a lamp module. With that and UPstart you can do a quick survey of your home. The software will give you signal strengh infromation around you home. UPB is a robust protocal that can work trouble free out of the box. There are a few items that can cause a problem but most homes do not have them. Devices with large capacitors such as whole house power backup systems. As you probably have read a few here have had problems with outside interference.
Dave