GET variable from URL (plugin/conditional) !!

[DrHUS]

Hello,
i use postbit_legacy by default on my forums, for some purpose i need to show the postbit (classic one) JUST by using Var on link
some thing like
showthread.php?t=36397&postbitstyle=classic
so thru the link above the user will show the classic postbit
other than that it will show them postbit_legacy

i do this global_start plugin (as i thought may will work) but it doesn't

PHP Code:

if ($GLOBALS[postbitstyle] = 'classic')
{
$vbulletin->options['legacypostbit'] = 0;
} 


also,
how can i make some conditional get the Var from URL

some thing like:

PHP Code:

<if conditional="$GLOBALS[theVar] = 'ok'">
blablabla
</if> 


so when some one call showthread.php?t=36397&theVar=ok
will show them the blablabla

can you help me !