Readme:
Create a new folder, Corvette in your art/units folder and unzip all the files to that folder. Then copy and paste the CorvetteLarge.pcx and CorvetteSmall.pcx into your art/civilopedia/icons/units folder. Then open up the Corvette32.pcx with an image editor, back-up your units_32.pcx and open it with an image editing program. Paste the image into a square at the end of the other icons, be sure to line it up correctly. Finally, backup your PediaIcons text and Civilopedia text. Then copy and paste the appropriate text below into its respective places (feel free to change the Civilopedia description, this is only my version). Finally, open up your scenario in the civ3-editor and add the unit (if you need help with this part, look around in the tutorials forum, I made this quick tutorial because some people organize their units differently).

Enjoy! 

Note: This is the second edition of my old Corvette, if you downloaded the old one, you can just paste this one over it.

PediaIcons

#start units
art\civilopedia\icons\units\CorvetteLarge.pcx
art\civilopedia\icons\units\CorvetteSmall.pcx

# Unit animations
#ANIMNAME_PRTO_Corvette
Corvette


Civilopedia (Age of Sail: 1st Generation)

#PRTO_Corvette
^
^
^ [Corvettes] are fast and light, making them excellent for hit and run missions. Corvette's aren't the strongest sailing vessel, but can dominate over Sloops and Privateers. It's speed and offensive power make it an ideal "Pirate Hunter". Corvettes are also fairly cheap, costing not much more than a Privateer.  
^
^A coastal city needs both $LINK<iron=GOOD_Iron> and $LINK<saltpeter=GOOD_Saltpeter> in its
$LINK<Strategic Resource=GCON_ResourcesS> box to build a Corvette.
^
#DESC_PRTO_Corvette
^
^ Corvettes are the "workhorse" of the modern navy. They are designed for high speeds and excellent maneuvering, forcing them to have less firepower than a Monitor but not so much as to make them weak. A corvette has 18 cannons and three masts, plus a bowsprit, with three sails on the fore and main masts and two on the mizzen mast. Corvette's are medium sized vessels, dwarfed by Man-O-War's and Ships of the Line but also dwarfing Sloops and some Privateers.
^ 
^ These vessels main role is support. A Corvette can distract a larger ship for much longer than a Privateer or Sloop could, and perhaps even deal out significant damage of it's own accord before a larger vessel can take over the fight. Corvettes also make excellent escorts for transports, and only four or five Corvettes are generally needed to provide complete protection from all ships excluding a Trident. The reasonably low cost of a Corvette also makes it an excellent vessel to make navies with, and can be produced very rapidly by a developed city. On their own, these vessels are commonly used for hunting down Pirates and/or Privateers, a mission that captains are all very enthusiastic in accepting. Many great navy admirals are created from service aboard Corvette's, giving these vessels a very prestigious reputation and making them the pride and symbol of most navies. 


Civilopedia (Standard)

#PRTO_Corvette
^
^
^ [Corvettes] are small, sailing warships widely used in the 18th and early 19th centuries. They are fast but not heavily armed, making them good hit-and-run vessels.  
^
^A coastal city needs both $LINK<iron=GOOD_Iron> and $LINK<saltpeter=GOOD_Saltpeter> in its
$LINK<Strategic Resource=GCON_ResourcesS> box to build a Corvette.
^
#DESC_PRTO_Corvette
^
^ Corvettes have between 10-20 cannons on a single gun deck, and three masts, since having less than three masts would classify it as a brig or civilian sloop. As time progressed and guns became more powerful a corvette was generally defined as a ship bigger than a gunboat with all cannons on a single gun deck. Corvettes can also be classified as Sloops of War, which remained a standard ship classification until after the second world war when they were fully replaced by frigates.