dvi, vga? please help

i have a lg 37 inch full hd LCD tv with a native rsolution of 1080p and i have my computer hooked up to it, the specs for my pc are...
intel quad core q6600
asus motherboard p5q
4gb ram
800w ps
nvidia geforce 9800 gtx oc

i have connected it using a dvi to hdmi cable but the image seems extremely crisp and the colour doesnt seem to good (not too bad when watching a movie), i don't get any overscan though.
i have also connected using a dvi to vga dongle and i get a much better picture than using the dvi to hdmi, i was wondering how this could be, i thought dvi was the conection of choice for hd.
anyway my problem is that even with vga, although the quality is far more superior than dvd quality for example, i don't believe i am getting it as good as it can.
are there any special players to play hd content on the pc? right now i'm using vlc player.
sory to go on and on!
thanks!

To answer the media player question, I use K-Lite mega codec pack. It comes with media player classic and has played every format I have attempted (including HD) and renders video better than any other player I have used including the expensive ones.

Hi KentWayne,
indeed you should get good results with a DVI-HDMI connection. I have my system hooked up like that and my htpc gives out a picture in the same quality as my standalone HD DVD player.

How does your HD picture look, when you watch HD material on a PC monitor? Is everything set to default levels in the video card driver settings? I've had some nvida driver versions in the past, that messed up color/gamma settings for some reason.

Have you tried other HDMI inputs of your TV?

Does your video card send out a 1920x1080p resolution to your HDTV?

(You could also use testpatterns like a greyscale to calibrate your HDTV. But you should at least get a decent picture by connecting your pc with the dvi/hdmi cable and only need testpatterns for finetuning imo.)

yeah it sends out 1920x1080, it is a 9800 gtx oc which i have been told is a good one and I think i have had some progress, i have downloaded a tv episode onto my pc, a hdtv rip in mkv format and it looks better than the 1080p files i have on my pc, could this simply be a case of a bad file compression? also if i put a bl ray drive in my pc i suppose then the quality should be amazing right?

p.s.
just thought i'd add, the monitor is a LG LCD 37LF65.
And still getting a much better picture using rgb than dvi-hdmi

hi, i've been away for a while so havent been able to check in. Anyway, i still have the same problem, vga gives a good picture, dvi gives a not so good picture, i don't see how this is, my pc is a quad core q6600 on a asus p5q mootherboard, 4gb ram, geforce 9800 gtx and my screen is a lg lcd 37" model 37lf65.
upto now i have been playing downloaded content at 720p and 1080p, i will be adding a bluray drive very shortly, will i get the full experience if i stick with the vga connection? also i have a component hdtv out socket in my graphics card, would that be better on my hd screen than vga? i have sort of given up on the dvi to hdmi connection

Down the line you will have an issue playing Blu Ray movies with VGA. On an HDMI Cable it conforms to the standard known as HDCP or, High Definition Copy Protection. My next upgrade will be to an Nvidia 280 bucause it is actually an HDMI vid card. I would double check the output resolution, refresh Hz, and make sure that the contacts are firmly in place.