CO2 Setup advice

[JutH1685 at aol_com]

I have been asked to convert a dentists poor saltwater setup to freshwater 
becase all his slat fish died.  My mom works for the dentist so thats why he 
asked me.  I was thinking of doing a small co2 setup for his 55 gal tank and 
i wonderd what you guys thought about my plans.  

TANK:
mailorder from harbor freight
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=5313
this tank is 5lb (i think) and i specific for co2
price $69.99

REGULATOR:
mailorder from harbor freight
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=47259
price $29.99

free shipping from harbor freight

NEEDLE VALVE & CO2 RESISTANT TUBING:
mailorder from floridadriftwood.com
http://www.floridadriftwood.com/product.asp?0=217&1=252&3=51
needle valve price $19.50

DIFFUSOR:
mailorder from pet solutions catalog
the eihem diffusor is $19.50 from the catalog

do you guys think this is a good setup?  do you foresee any problems?  Do i 
attatch the regulator to the master valve supplied on the tank, and then the 
needle valve to the regulator?

any tips are greatly appreciated!!
thanks, justin
juth1685 at aol_com