here is a link to CPUZ-ID it will identify your cpu and tell you what instructions it supports.
http://www.cpuid.com/cpuz.php
AMD USERS NEED AT LEAST A AMD64
PENTIUM 4 on average 1.4 ghz or above has sse2 but i wouldnt use any of these new version on that kinda system.
The new version was really designed for HD While allowing you to still do SD or DV video's
but still download that program and check what instructions your cpu supports to be sure
This is probily one of the first adobe's in a long time that when they say you should have cirtain hardware to run they mean it.
So if your planning on getting it for your old 1.6ghz p4 dont bother stay with a older version. same goes for those with older amd's
My advice is have at least a 2.8ghz pentium or a nice amd64 3200+ cpu and you should run it just fine.
PEOPLE WITH 2.0GHZ P4'S CAN STILL RUN IT BUT ENJOY THE LAG