Forza Motorsport 3

All the driver level achievements will be gained as you progress through the season career. Every time you finish a race you gain xp. It is best to win the race as you get more xp. You should get this around Year Three of the career mode (if you win enough races). Every time you rank up your driver you get a free car, as you progress through the career mode the gaps between levels increase but the xp for winning races also increases for the longer races. It will come it just takes time.

craig killed ya has a very god guide for this but an easy way to get this and the driver level 30 is to simply go on the event list because at level 20 you unlock the endurance races thes will gine you around 100,000 xp each and will level you up from 21 to 25 from 25 to mid 28 and from 28 to just under 31 easy levels, happy gaming