I will be surprised if vb2 doesn't work with php3 when it's released.
You might want to play with vb2 beta3. Here's what I do, I create a private directory on my server that has a backup copy of my vb database. Before I hack or install new hacks, I test them on that directory until I'm happy.
You can test vb2 in a similar way by doing a global search and replace for php to php3 and then rename files to php3 "mv *.php *.php3"
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