What resolution do you use on the Samsung 52" LCD?
What is the make and model of your current PSU?
IF you need to upgrade your PSU, the one recommend by benski is a good choice.
IF your Samsung resolution is 2560x1600 or less, then I recommend going with the GTS 450 - like this one for only $90 after rebate:http://www.newegg.com/Product/Product.aspx?Item=N82E16814130572&cm_re=gts_450_1gb-_-14-130-572-_-Product
The 5770 is a little faster and if the price is better or not to much more it would be a good choice too. However if you use Adobe Photoshop or do much video editing or encoding, you might take a look at the nVidia advantages of CUDA and Physx.http://www.tomshardware.com/reviews/adobe-cs5-cuda-64-bit,2770-8.htmlhttp://www.tomshardware.com/reviews/asrock-e350m1-amd-brazos-zacate-apu,2840-5.html
You might also want to look at the non-gaming page at upgradevideocards.com that has additional info and links to other articles about HTPC that you might find informative.http://www.upgradevideocards.com/nongamining.html