Here is an small guide on installing firebird odbc driver from source (alternate you can install it from binary repository )

A good reference to unixodbc is located here
First step is to  have installed unixodbc on fedora:

yum install unixODBC unixODBC-develop

and on ubuntu (debian):

sudo apt-get install unixodbc unixodbc-dev

then checkout the odbc driver :

cvs login
cvs -z3 co OdbcJdbc

cd OdbcJdbc/Builds/Gcc.lin
make -f makefile.linux

Next read the readme.linux

driver seems to be in directory OdbcJdbc/Builds/Gcc.lin/Release

cd OdbcJdbc/Builds/Gcc.lin/Release
sudo cp *.so /usr/lib
sudo ln -s /usr/lib/ /usr/lib/IscDbc

create content in the folowing files
cat /etc/odbcinst.ini
Description = Firebird ODBC Driver
Driver = /usr/lib/
Setup = /usr/lib/
Threading = 1
FileUsage = 1
CPTimeout =
CPReuse =

cat /etc/odbc.ini
Description = Firebird
Driver = Firebird
Dbname = localhost:/var/lib/firebird/2.0/system/help.fdb
Password = masterkey
Role =
CharacterSet =
ReadOnly = No
NoWait = No

isql -v help
| Connected!                 |
SQL> select * from topics;

ps: i assume that firebird and g++ are already installed on the system