You can play ordinary DVDs and they will be "upscaled" by an ordinary DVD player that is HDTV compliant and connected to the TV by HDMI (High Definition Media Interface) cable - you will notice a significant improvement in quality. However, as others have said, for true High Definition you will require a BluRay player which will play special BluRay disks - however these disks are significantly more expensive at present. A BluRay player is backwards compatible; it will play conventional DVDs as well and upscale their quality, though not to full HD standard.
HDTV - as a disk format rather than as a description - is dead now that Toshiba, one of the main backers and manufacturers, has conceded defeat to the rival BluRay after a majority of the film distributors voted Bluray in preference. Thus a similar battle of the formats to the VHS v Betamax war of the video formats has been avoided - except that this time Sony is on the winning side.
I wouldn't consider HD-DVD now as there has been a bit of news of late about a lot of shops/content manufacturers chosing not to be involved with HD DVD, and instead favouring the Blu Ray format. The Playstation 3 can play Blu Ray disc's!
I agree - that what I was trying to say in my final paragraph. HD-DVD is dead in the water and Toshiba are clearing out the last of their players at bargain prices, having ceased production. I wouldn't touch them with a bargepole as the media simply won't be available.
An HDMI compliant ordinary DVD player will upscale conventional DVDs and can be had for around £30 upwards. If you want the full works then its a Blu Ray player which will, at the moment, set you back just short of £200 at the bottom of the range - expect prices to plummet when the format becomes established. Or, as you say, go for a Playstation 3!
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