With a 250w PSU you should be OK up to an AMD HD5570 or an nVidia GT430 - and these will handle 1080i content to a 1080p display with high-quality deinterlacing.
If you only play SD content then an AMD HD5450 would be OK.
Thank you, but don't forget that i need a half height card for my slim case. So do you know where i could get either one of these cards that is half height?
My system is in a slim case too - I use this Palit- GT 430 (1024MB DDR3) which comes with low-profile brackets, and Sapphire do a low-profile HD5570. There are lots of low-profile HD5450's around.
I'm using a 5450 and it's great. Passively cooled and it came with both full height and low profile brackets. Certainly has no issues playing back direct BD rips and HDTV.
Which nvidia model should I go for if my goal is exellent sdtv de-interlacing, good hd/br playback. No need for hd audio and 1080i. Currently using radeon 4550, but sick of flickering and HDTV corruption.