What I did was put floatval() around the entire line, like so:
$level = floatval(pow(log10($experience), $exprate));
Guess it has the same effect

And yeah, I would have to go with old PHP version too. But it's always nice to be backwards compatible
Im glad you enjoy the hack, and I'll be looking forward to having you with us even onto vB 3.5 and the new heights the hack will reach
//peace