I just checked the gcf files of steam, seems to be around 402MB. Unless I missed some files that are in combination with. I'll remove the image restriction for new users as I've made some modifications on the forums, and you are downloading Half-Life through steam, right?
You might want to either remove the clientblob file within your steam folder (close steam first), remove the whole steam folder & reinstall steam. Or, check your internet connection to see if everything is working correctly. How did you get the 800MB btw? Half-Life from the internet?