how do you record gameplay videos from your 360?

Ie on youtube you have high def gameplay vids of 360 games being played. How do you do this? Is it pretty simple or do you need to invest in some expensive equipment? If i have a pc and an xbox 360 how do i do this?

do you need a certain one to be able to do high def? Also i currently have my 360 hooked into my computer monitor through the hdmi port and switch back and forth so thats going to be a problem i assume. would i need to hook my 360 to a tv so i can see it when recording or will i be able to set it to record and hten switch?

youtube "gaming capture cards" and they recomend good ones...

If you are on an HD tv then you may have some trouble with this, but if you are SD then capture cards are easy