[akanevsky]

No, you may not access GPC from templates.
You must put
$myvar =& $vbulletin->GPC['myvar'];
if you want to use the variable in a template (note the "&" sign - it establishes a reference rather than copying the variable - for memory saving purposes).

Somewhere in the new version, similar code is being executed (though not with the deregister_globals function -- I grep'd for it), because the globals I've defined are getting cleared out.

You should not be defining globals unless it's after you've included global.php.