You've been lied to.
I'm using WPA with the Broadcom card right now on a Dell D800 and also on a D400. NDiswrapper and the Windows driver.
The internal card uses an antenna that surrounds the LCD, built into the case. Because of this, I've found the range on internal cards to be better (on average) than external ones.
Searching for the WG511 v2 gives mixed results - some say it's a Prism54 chipset, others say Marvell and some say it depends on the place of manufacture. lspci -v should tell you for sure, as it's a Cardbus card. They sit on the PCI bus.
If it's Prism54, you can get a Linux driver. If Marvell, you'll be stuck using ndiswrapper.