Okay, I got it working. This is something I've tried multiple times before with other IR receivers, but this is the first time it's been 100% successful... so kudos to you guys for Flirc. it seems to be the missing piece to my puzzle. :)
1) Using my generic Media Center remote, I recorded keystrokes using the terminal command line. (I picked the most useful from this list: http://wiki.xbmc.org...?title=Keyboard ).
**Because I'm using a generic MCE remote, I had to record each keystroke twice in the command line to avoid pressing each button twice in XBMC, per this thread:
2) In the Harmony software, I created a device, "Flirc," based on a generic Microsoft MCE Remote (Computer > Media Center PC > Microsoft > MCE Remote).
3) In the device settings, I created a list of custom IR commands (at the bottom of the page); I simply named them after the keystroke they emulate (X, P, Spacebar, etc.). The only default IR commands I used were the directional commands.
4) Using the Harmony remote, I learned this set of custom IR commands from the MCE remote.
5) In the device settings, I customized the Harmony remote buttons by assigning them to the newly-learned, custom IR commands (Menu = M, Pause = Spacebar, etc.).
6) In the Harmony software, I created an activity to turn on my TV, set it to the correct input, and select my Flirc device.
7) In the activity settings, I once again customized my Harmony remote buttons appropriately, assigning most to the Flirc IR commands, and others, such as volume control, to the TV.
8) ????
9) Profit!!
I now have a 100% working Harmony remote with one-touch access to my XBMC setup. Well, almost one-touch... I'm still trying to figure out how to use the Harmony remote to turn on my HTPC or resume XBMC from sleep... but that's another headache for another day.
Hope this helps.