Barbara,
Sorry to be the bearer of bad news, but you are unlikely to get another program which behaves significantly better on all fronts. PowerDirector is simply a bundle of software which makes logical decisions, based on the interface and tools it provides - just like any other video editor - and then does the 'rendering' part. This rendering part tends to take the same-ish amount of time, whatever the software overcoat written around it - most editors use the same codecs to do the job.
Without suggesting that PD9 is without any bugs, I have to say that most of the things I have got hot under the collar about have turned out to be due to the interaction between PD9 and its hardware/software environment. Just because PD9 doesn't work with the latest driver from XYZ doesn't meant that PD9 is necessarily at fault ! It is just as possible - and it often occurs, really often - that the XYZ driver is the problem: the designers fixed something over here, and trod on something over there in the software.
Since most video shot will not actually be of HD quality, even though shot in HD, I would suggest you work a little less ambitiously. Try using 720 rather than 1080, or even use SD and produce for DVD quality. This wil sort-of make your computer more powerful in relation to what you are asking, and you may get a better handle on what is going on.
I used a 3.1G Pentium based platform running XP, and found it just couldn't do the job, stuttering and freezing all over the place. One of the problems I encountered was that a client program asked for something, the operating system took so long that the client timed out, so was unable to accept the reply eventually, but the client then hung. Guess what was the client program?
i7 980x; W7 Pro; 12GB; Nvidia GTX 285; 2x300G Velociraptors in Raid 0; 2x1.5TB Barracuda in Raid 1; 2TB WD Studio Ed.II (eSATA); NEC SpectraView Reference 2690 + MultiSync EA232