you have to edit the drivers.ini in gpxpdata folder with the prefixes for your driver names and countries like the example below and you have to insert the flags folder in gpxpdata\gfx\digital2010, that's all
[Juan-Pablo Montoya]
code=MOY
country=CO
[Michael Schumacher]
code=MSC
country=DE
[Kimi Raikkonen]
code=RAI
country=FI
[Valtteri Bottas]
code=BOT
country=FI
[Tomas Enge]
code=ENG
country=CZ
[David Coulthard]
code=COU
country=SC
[Jenson Button]
code=BUT
country=EN