Furry, I am not sure what series Sony LCD projector that is, but here's a few tips from mine (Sony 55" WF series), which works perfectly with a 720P resolution sent to it from my PC (also with DVI to HDMI cable).
First, find out the native resolution of your tv, it probably is a 720P, which means that 1080i input is downconverted to 720P. This also means that the LCD's in it are probably something like 1300x760 or thereabouts, so higher resolutions out of your computer are not of much benefit. Also, by feeding it 1080i, you are only doing 30 fields per second which results in picture jitter in panning scenes. Now if that thing is one of those 1080 Progressives, thats another story. Best to set your video output at 1280x720 to match this. Setting a custom resolution in powerstrip will not work, as the Sony only likes true 1080i or 720P as an input. The tv will not display any other resolution fed to it by the video card. (Note, depending on your video driver, you might be able to cram another resolution to the TV, but that resolution is scaled into whatever HDTV format resolution by the video card anyway when set to function with a HDTV)
On the overscan, you will need to go into the service menu for the adjustments. Fairly easily done and you can adjust the TV perfectly with no overscan with a computer input. If it is like my Sony, you dont have to worry about goofing up the TV doing this, as each input has seperate overscan settings. Go to avsforum.com and check in the LCD projector TV forum for a thread that covers your model, you will find all the info you need there.