If you go on to the stvplayer rather than the itvplayer you should be able to watch all the itv programmes, it doesn't come up with the messge about flash player on that site.
I bought a Boxee Box about two months ago and am still waiting to be able to actually use it. I thought it was becoming more painful than worth it!
First of all, I had problems actually selecting any programmes on the iplayers chosen - this was fixed by asking the Boxee support team - I had to upgrade my Boxee Box ...
Now my problem is, it isn't compatible with Adobe Flash (yet) and I wanted to watch Xfactor last weekend and couldn't as I needed flash .... aaarrrgghhhhhh
So have now logged another issue with the support team. Apparently the rumour is in their next upgrade they will install flash player ..... who knows!
My friend has one and swears by it and uses it all the time and loves it ...... I am looking forward to mine working in the same way and loving it same as her. Maybe in time for Christmas .....