Is it ok to install the latest JDK to run IntelliJ-IDEA as well as have VS 2008 on the same machine?
Yes. The two will not cause problems with each other.
Yes. Java doesn't have any dependencies on the .NET framework and vice-versa, so you shouldn't expect any problems.
i have eclipse, intellij-idea, netbeans and vs on the same machine and i did not get any problem just because of this.