to unlock the unlockable factions goto:

C:\Program Files\Activision\Rome - Total War\Data\world\maps\campaign\imperial_campaign

then open the descr_strat.txt file

you will then see:

campaign imperial_campaign
playable
romans_julii
romans_brutii
romans_scipii
end
unlockable
egypt
seleucid
carthage
parthia
gauls
germans
britons
greek_cities
end
nonplayable
romans_senate
macedon
pontus
armenia
dacia
scythia
spain
thrace
numidia
slave
end

change this to:

campaign imperial_campaign
playable
romans_julii
romans_brutii
romans_scipii
macedon
pontus
armenia
dacia
scythia
spain
thrace
numidia
egypt
seleucid
carthage
parthia
gauls
germans
britons
greek_cities
end
unlockable
end
nonplayable
romans_senate
slave
end

this should work!!!

cheers

NB: i can't get the spaces right but you will see what i mean when you open the file