Hi
I have done a few of these for insurance companies (people normally claim through insurance as it is a long job and can cost quite a bit).
You will really struggle to remove the paint using cold water without damaging the surface of the tarmac.
To get good results you will need to use steam, but this too has its dangers as you can easily melt the tarmac.
Basically, you need to be really, REALLY careful.
In some instances, it can prove impossible to remove it entirely and in these situations the insurance companies have asked me to re colour the drive which has been very successful too.
I hope this is of some help.
Andy
Take a look here
http://www.afsystems.co.uk/index.php?action=more&type=gallery&gid=66&id=121 for an example of what can be done - no colour was used on this job, just steam cleaned. This drive was completely covered in splashes of paint and looked like the first photo all over. A.