Yep, a power meter is a massive boon to time trialling training - not just for training but for also determining aero testing.
That being said there are plenty of ways of doing it without a PM.
The training for a time trial is not that dissimilar to any aerobic cycling training with the one exception being that I fully encourage training in the time trial position regularly- and actually training the position
very aggressively. This means spending a lot of time tweaking the bike and tweaking (NOT twerking!) the body to be in an effective position for aerodynamics and power output. Stretching (if you are actually inflexible enough, very few are), and general "conditioning" to hold the arms, head, shoulders in a tight position.
You can sacrifice power for aero... if you're a LOT more aero. And you'll only know that through testing. So I have all manner of mirrors and a camera on a tripod to record hard efforts in the TT position to check that the body is solid, arms are narrow, head is down etc. This is then checked and double checked through testing to make sure it is fast. Aero gets a "bad rap" sometimes, the amount of times I've heard or seen stronger riders "dismiss" the finer points of a good time trial setup and then complain when they get beat - then you see the photos - head up, looking far ahead, parachute chest, huge cable loops, flapping skin suit (wrong size), helmet/body interface all over the place, wide shoulders/arms etcetc.
Alex Simmons has this excellent chart for a "ready reckoner" for performance of approximate w/cda. http://s220.photobucket.com/user/ASimmo ... 6.jpg.html
As for the actual training, as mentioned above, not a huge amount changes. I generally prescribe either a lot of volume well below FTP or FTP and above. I even very occasionally have short "sprints" programmed - in the TT position of course!
As you may have seen from past threads a basic week or two programme can work very well... until it doesn't. The favourite 2x20mins are good, but not the only TT training tool in the box.
Also the other big boon to time trialling is the pre race "ritual". Get into a set program of how you setup and prepare for a TT and do every TT in the same way. This helps the mental aspect and preparation and helps control the mental arousal before starting.
Depending on the distance most of the training will be largely the same unless you're going for some stupid 160km TT, only an idiot would try that distance... twice.
Oh and the last bit of advice for ANY TT... don't start too hard.
Any questions, let me know.