is there a screen size limit to cards like the 5970?
i have a samsung pn42b450b which is a 42" plasma tv and is 720 P
since the 5970 can do 1080 P does this mean i can plug my computer into this tv via the hdmi port?
if there is some info you need just tell me ill look it up to see more specs.
As far as the connection goes, that's easy - yes you can just connect your graphics card to your HDMI port using a normal HDMI cable. If your graphics card doesn't have an HDMI port, you might need a converter but most boxed graphics cards come with one these days.
The size of the monitor makes absolutely no difference to a graphics card, it's all about the number of pixels it's being asked to produce per frame. Your TV is 720P, so will probably run at either 1280x720 or 1366x768. This means for each frame it will need to produce 921,600 or 1,049,088 pixels. Most PC monitors above 20 inches run at 1920x1080 or 1920x1200 - 2,073,600 or 2,304,000 pixels - way higher than you're asking your graphics card to produce.
The 5970 is designed to run on monitors of up to 30 inches (2560x1200 - 3,072,000 pixels) or even 3 monitors simultaneously at higher resolutions than you're asking it to run 1 at! You will almost certainly be able to save yourself LOTS of money by going with a graphics card more suited to a 720P output - the 5850 would be able to do this without breaking a sweat.
Remember - the important thing is how many pixels you're asking the card to produce, not how big each pixel is then displayed.