No, You need two radios (read: two miniPCI cards). Since the WL500g only has one Mini PCI slot (unlike e.g. the D-link
DI-774 wich has two) it became a 802.11a only box.
BTW I will use one of the DI-774 MiniPCI cards for the WL500g as well, since these cards are based on an Atheros chipset. The WL500g has native support for this chipset (although the driver is not included, only the control files are). It is a good exersise to port the madwifi driver to the Mips platform, although our goal is to port it eventually to our ARM 9 platform.