I am having a similar problem with my 1.2 xbox w/ Samsung dvd drive and western digital 250 gb hdd playing games off of the hdd, some freeze. However playing the original disk is no problem. I thought that the backup might be corrupt so I took halo 2 and put it on a software modded xbox via FTP and to my surprize the other xbox plays the backup with no problems.
Mine will start all of the games just fine but then while playing the game it will freeze sometimes with an audio loop. So far I have noticed the problem on bloodrayne 2, i-ninja, halo 2, and the simpsons hit & run, but have not had the problem in burnout 3, the incredibles, or x-men legends. Hopefully this is a bios problem and a new bios release will fix it. hopefully.