QuickTime Slow with AMD?

[Gaidal]

Hi guys, I have a AMD Thunderbird 950 and an Asus A7V with plenty of RAM (256) and a fast hard drive (7200 rpm). Anyways, I noticed that Quicktime movies seem to play awfully slow on my computer. For example, I tried to view the XL sized trailer to "The Lord of the Rings" on the website but it played stuttery and jittery and I could only see it smoothly by moving down to the Medium sized one. This is kind of disconcerting to me because I could view the XL trailer with full speed and everything with my old P2-400. Is this a problem everybody has or do I have a setting wrong? Thanks!