I agree that you can not become 'fast'.
After injuring my ankle long back, I lost all the speed I had. No matter how much I trained and practiced, I could no longer run as fast as I once did. But what training did improve were my bursts.
And in football that is more important than running fast. After some focussed training, I saw myself beating the players to the ball as long as it was on a short distance.
If you can do this as a defender or a striker, it will work to your advantage.
Anyways, I play just behind the midfielders and usually sneak up front as the game builds up.
Even as a midfielder, I can burst into positions.
You have to appreciate that positioning is very important, it can help you make up for your lack of speed.
There might be barriers of speed that you may not be able to break no matter how much you train. But if you can always improve your bursts and reactions.
Just take a look at Ronaldo (the 'real' one). He may be fat, but you still can see him beating defenders to the ball with his ocassional bursts of speed.
If you are looking to improve your balance, acceleration and agility then go through the fitness forums, there are loads of exercises there that will help you do that.
If you want to improve your 'turning' then that will need some patience and focused training on your side. I learnt to do the 'shimmey past defenders' after watching Ronaldo do the same on video for hours. Then I went and practiced it alone for nearly three weeks. Then I tried pulling it off in matches.
Anyways, all the best.
PS: Were you joking about Rio Ferdinand ????