Hi, and welcome to TSF. I'm afraid not. Not only are the connectors physically incompatible (they should be, anyway), but the PCI-Express/ExpressCard bus is a completely different architecture and in a completely different bus location than PCI/CardBus. Unfortunately, Dell has taken the initiative of attempting to "phase out" CardBus over ExpressCard by excluding CardBus slots on its machines, despite its obvious functional prowess over ExpressCard... Manufacturers like Toshiba and IBM currently include one of both slots. Sorry about the bad news...
-Ed
-Ed