there is documentation on backing up index and configuration data here:
as long as both your 32-bit and 64-bit systems are x86, then you should be ok moving your indexed data.
it would be useful to have a topic that specifically addressed the overall task of moving a Splunk installation from one machine to another, i will make sure that happens.
Another idea is to install Splunk fresh in your Win2k8 64bit box. Stop sending data to the 32bit box. Then:
Option 1: Copy folders var and etc from the old box to the new box. Make sure that the file permissions are the same. Hopefully these boxes belong to a DC so that you can login as the same domain user in both boxes when you copy the files over. You also you'll need to copy your splunk license file over to the new box.
Option 2: Setup these two boxes as a distributed Splunk deployment, with two indexers, your old box and the new one. If you make the old box the Search Head, then you'll have old data and configs, plus your new data will be in the new box.
Copying data around it's little tricky with windows, give the file permissions and all.