As long as you have a certified JVM you should have no problem. I have been running JBoss AS 5 for the past several months on a 64-bit Vista system running both 32-bit and 64-bit JVM without issue. I have also run on 32-bit Windows 2008 without issue.
But make sure you use the latest JVM - when Vista came out the current versions of the JVM at that time were not very well behaved. But you should have no issues with 6u7, 6u11 or 1.5.0_16.