I can't install the drivers under windows 64
The last tiime I looked windows 7 was the last version number I seemed to have missed 57 versions 
OK, seriously,
which version of windows do you use? (64 bit obviously 
which version of IDE you try to run?
What Arduino are you installing
What type of PC are you using?
What is the error message?
What appears in the windows log files?
Have you read - http://www.arduino.cc/en/Guide/Windows - very carefully ??
in short there is too much information missing to help,
Normaly I run ubuntu.
I have a book, "getting starting with arduino, there I read linux is more difficult to install. So I try to install it to xp, but with no success.
Yesterday I uppdate ubuntu to 11.04 and the installation was wery easy. I loked in the software center and aurdino was there. So I installed it all with a mouseclick.
And now it run with no problem.