Video Card recommendation for HTPC

I have a fairly new Dell PC (bought about a year ago) with the stock on board video card – I think Intel 3000 (I have to check))- anyway, it often freezes during bluray playback, and is sluggish when I open close HD videos recorded on my Windows 7 Media Center. I’m thinking of getting a new video card (if you think that will help) – which ones would you recommend – I don’t do any gaming, all Home Theater use.
How is the EVGA GeForce GT 640 2GB – I saw it on sale, and was wondering how well it would fit my needs – or if there’s a better value out for my needs.
Also – I am thinking about getting a 3D projector – which video card would support BluRay 3D to a 3D projector?

Correction - I have he Intel HD 2000
How do I trouble shoot?

I ran realtemp - no issues
I am over 100 processes -
Also - another oddity that I notice, although the PQ is great, one weird thing is that even when wokring "fine" very often there will appear to be as if the image is rewriting itself on the screen - i.e. the image looks fine, but it almost appears as if there's a horizontal line which makes it's way from the top of the screen to the bottom then disappears until it comes back later - it's not an actual black line , but rather the image itself causing the appearance of a line going down.

Lastly ,I have 4GB of RAMin my machine - how much of it should I dedicate for the video card?