As the owner of a steam-powered PC :
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I'm well used to not being able to watch the HD stuff (1.7G CPU with 1G ram Win XP) with any player (although good old VLC does a fair job).
I have no problems burning them to DVD with Nero 6 and the quality is still as good as any standard DVD (I also have nothing HD capable so no Blu-ray or HD TV) so if you are not already enjoying Blu-ray then you won't notice ;D
If you want to watch them on your laptop or slower PC (as I do), save the original HD file somewhere save (external disc or, better still, a data DVD) and use a free program (like Super) to downgrade them to something you CAN play on what you have.
That way you can watch them on your PC and you still have the HD files safe (in case you upgrade things at a later date). You may have to try a few times to find out what your PC will cope with.
As Dajatje says, burning HD to a standard DVD will make the DVD SD so you should be able to play it on a standard DVD player as it is no longer HD (finalize a DVD-R and make compatible but a DVD-RW should play fine right from the burner). The DVD player probably won't play the raw data files (ie just a straight copy of the files you downloaded) unless your DVD is capable of playing that format (mine plays avi files fine but won't "see" Divx etc. Need to look in your DVD players handbook for what it will play.
Been there, done that, got the tee-shirt :
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)