Upgrade to CS6
AMD chips are not ideal. Need a fast disk raid array media.
Hate to say it but a new computer might help.
Does CS6 run off less powerful machines like Mine?
Yeah, you have a good point there. The Adobe Mercury Playback Engine that drives PP real needs fast Intel chips, lots of ram. a powerful GPU and a fast raid array to really perform at its best.
Now if when you exported your movie from AE you made it the exact same format / codec as your PP timeline, you shouldnt have to render it at all when playing it back on the PP timeline.
What kind of media are you working with here?