Planning my first tour

Hello,

I have been a bicycle commuter for the past four years.  I enjoy cycling 
so much that I am now planning a tour of the south from San Francisco to 
New Orleans.  In planning I have quickly come across a rather important 
detail:  I need a bike!  At first I thought I could simply load up my 
1970s Shwinn steel frame roadbike with some panniers and be on my merry 
way.  It appears that a larger investment is necessary though.  Can 
anyone provide advice on where to look for a touring bike?  They seem to 
be a rare breed, at least compared to other styles.  I am open to buying 
a used bike initially.  Is anyone in support of this?  Also, there is a 
website: bikesdirect.com which has discounted bikes of which I am not 
sure of the quality or applicability when it comes to touring.  If a 
used bike or discounted stock bike is not appropriate what brand frame 
and wheels should I be looking for?

thanks for the help,

vince