Hey....The B5 only ran from 2000-2001. Well, 2001.5 I believe. As far as making it 11 it an 11 second car...it depends on your budget. You can either.
A.) Build it into an RS4. And, then tune the hell out of it. 500hp if done correctly.
B.) Swap everything out for a GT28 or 30 turbo setup. Easily looking at 500hp if tuned right
C.) You can build it from the S4 platform like I have done. I'm not quite an 11 second car, but I'll be there soon. Start with a ECU upgrade(MTM, APR, GIAC, etc), then a downpipe replacement(APR, Milltek, or Vast makes a good piggy pipe) intake(Not neccesary though, the stock is great as it is. But if you do replace...find an X1 Racer CF intake :-D) You're going to want to do the rest of the exhaust as well.(APR, Milltek, Vast, or a custom setup) Next, depending on the trans you're going to want to either - replace the clutch and components or find a TCU chip for the tiptronic(I highly recommend them) That should get you to about 330-340hp. I'm running all that right now and I'm in the mid to high 12's. To get more, you'll have to replace the fueling system with the RS4 setup.
Either way you go, don't forget the rest of the car. Get a nice brake upgrade. The kits are a bit pricey, but well worth it. And, upgrade the suspension and check the control arms and front end.(Ball joints, tie-rods, etc)
With any of them, you should be well on your way to an 11 second B5. They're sweet cars, and I'd suggest one to anyone. I'm not sure what you're looking at cost to do it though. All I know is I have about 18k in aftermarket work done to mine now. And, I'm not to an 11 second car yet. So, good luck to you.