Forza Motorsport 2

My advice is to beat one of the first events where you win the Porsche 1970 416 (Index 196). Dont add any parts! Take this car and use it in the European race under proving grounds at easy difficulty, and you should be able to win.

Alright, there's a lot of good advice given here, however they don't say what race to do.
I was able to knock out this and the "Hard Charger" achievement in one go. What you'll want to do is buy the VW Golf GTi Mk2 and race in the "Hot Hatch Runoff" playlist in the "Proving Grounds" tab. You have to be a lvl.3 to get into that playlist, but it doesn't take long to get there. also you'll want to set the difficulty to the lowest. By the end of the first lap I was in 1st place. Oh, and it' the first race in that playlist. :D
Good Luck, I hope this helps.

Another solution if anybody is playing this game anymore is when you first start a career select the VW Golf GTi Mk2 and don't add any parts. Put it on Novice and you should get this achievement plus the Hard Charger achievement in the first race.

I just received this on accident while in the semi-pro races on the Suzuka circuit.

I used a stock 1996 Chevrolet Corvette Grand Sport and kept up some decent lap times, then boom, achievement.

Try using some different cars (make sure they're stock). They have to have a low PI but not so low that they can't keep up as there are some very quick cars in this race. I'd also suggests turning the AI difficulty to low.