Congratulations on your new adventure in to 3D!
Firstly, I would like to mention that hdmi will NOT accept a 120Hz input. Since the Xbox360 uses hdmi as its best connection, I would suggest hooking it up directly with hdmi and connecting the pc using a dual-link dvi cable or displayport. According to your manual (p.78), only the DVI and DP inputs support 120hz:http://downloadcenter.samsung.com/conte ... 5A-Eng.pdf
TriDef an Iz3D are pretty much your only choices when it comes to a Radeon card. It has been a long time since Iz3D has seen an update so TriDef is probably your best bet. Make sure your driver is up to date; you can check the TriDef forum for beta drivers that may increase performance. Once you have the correct connection to your monitor, make sure you have it set to 1080p Frame Sequential. Personally, I use Nvidia 3D Vision and feel that it is a more polished product, but AMD is starting to get there. TriDef has a good community which churns out compatibility profiles for new games fairly often.
As far as movies go, Stereoscopic Player and PowerDVD come highly recommended. There are free trials out there for you to find which you prefer. I find that the newer versions of PowerDVD have a lot of useless bloated features so I stick with v10 if I want to play a 3D Bluray, (or use my PS3, which has many more 3D games as well). I also tend to avoid the automatic 2D>3D conversion tools as I find them gimmicky at best and usually prefer to find native stereoscopic content.