beginner tri-bike wanted.

I'm 6'8".  I picked up a 63cm 735TT tri frame from Leader Bikes (www.leaderbikestore.com).  I'm very happy with the bike.  I did have to build it up myself, though.

Many manufacturers make sizes up to 60 or 61cm.  Look at the Felts for example.

The 63cm frame has an 18cm head tube.

The Leader store site does have the dimensions of their bikes.

http://www.leaderbikestore.com/pd_ld_735tt.cfm

Here's a pic:

Leader has three TT models.  The 730TT is standard aluminum  The 735TT (mine) is a stronger alloy (and thus thinner/lighter).  The 780TT is the alloy with carbon seat stays.  The 735TT is the lightest of the group.  If I remember correctly, my frame was 2.8 lbs.  The Leader guys can tell you the actual weight for each size.

I'm not sure how that would match up with various full CF frames.  I'd imagine that some would be lighter and others heavier.  There are other reasons that some people go with carbon, though.  Quite often, it's the bling factor. 

I actually did cut the steerer tube down by about an inch, but left it long enough to fine tune the fit.  I'll trim it again once I'm certain it's where I want it.  I'm sure it would be plenty long for you, but you would need to get a LOT of spacers if you didn't end up cutting it.

If you buy a complete bike and go with the Profile Design Carbon X bars, the stem is integrated into the bar system and can't be swapped.  Just one thing to think about. 

22+ is pretty heavy.  I'm sure you could cut some weight off by swapping components to a different bike.  However, you may run into problems trying to do this.  At the very least, you will need to purchase the headset along with the frame and fork.  Also, you need to make sure the components will work.  I'm not sure if they will mount the same way.  For example, you'll need a braze-on front derailleur if yours isn't one.  Unfortunately, I don't have a lot of experience with bikes that are older than 2 years.

My recommendation would be to either save up for a complete new bike, or get the parts separately and build it up over time.  Or spend the money on a pair of sweet racing wheels, which you can then use on a new bike at a later time.

If you are looking for a complete new tri bike but don't want to spend a lot, take a look at the Motobecane Nemesis (www.bikesdirect.com).  A buddy has one.  At under $1k, you can't beat it, assuming that you can get a good fit on it. 

If I were to do the wheels again, I'd follow Bear's advice and put a Renn disc on the back and a HED 3 spoke on the front. 

I got mine used on Ebay for about $600 and am pretty happy with them.  They are a good balance of aerodynamics and weight.  But they aren't quite as fast as a rear disc would be on a flat TT.

When you are ready to purchase the Leader frame, give them a call to talk it over with them.  They will be happy to talk sizing and the techincal aspects of moving the componentry over. 
 

I'd also suggest investigating Guru.  They custom build each frame, out of aluminum or carbon, and were reasonably priced.  I'm a funny geometry (not giant, just different) and they measure you and build the frame up for what you need.  I didn't end up getting one because a Felt was just as good a fit for me... 

But I know they do great work...I know a Microsoft exec in Seattle (6'8", 325) who got fit for a Guru - and they build him a double-walled custom carbon frame, with significant bottom bracket reinforcement - for the same price as their stock gurus - it seems like the custom part is just part of their service. 

Ouch!

That's all I have to say about that.