The "Offline" installer for Java is always the best one to use. The regular online installer which installs over the internet not infrequently results in unreliable & corrupt installations. ie: you will see two options, one is much larger than the other & is perhaps 13.92 MB to download. Choose the large one (it says Offline beside it). After downloading, open it & install.

As for which version of Java 6, not sure. I am not a Vista user so can not give advice on the most reliable release so far for Vista. Download Java software from Sun Microsystems