Yes and No.
Cube Owners can use an Airport Extreme BaseStation as their wireless router, in order to take advantage of the USB printer sharing feature, etc... since the Airport Extreme's 802.11g spec is backwards compatible with 802.11b (standard Airport) cards. Of course your Cube will still be limited to 802.11b speeds, even with the Airport Exteme BaseStation. Unless...
MorganB reports that he is successfully using a
D-Link DWL-G810 Wireless 802.11g Bridge Adapter with a
D-Link DI-624 AirPlus Xtreme G Wireless Router (much better value than Apple's Airport Extreme if you don't need USB Printing over your wireless network). Morgan is using this setup to stream MPEG 2 with his Neuston Virtuoso. It works well for El Gato's EyeHome too!
The AirPort Extreme Card works with the computers listed below and requires Mac OS X 10.2.3 or later. Attempting to install it in a computer that is not on this list (such as the Cube) may damage the computer and/or the card. As you can see from the pictures below, the cards look totally different and are not interchangeable.
Here are pictures of the Airport and Airport Extreme cards and the computers that support them:
Apple AirPort Card

Figure 1
The Apple AirPort Card (Figure 1) can be installed in the following computers:
- iMac (Slot Loading)
- iMac (Summer 2000) - See Note 2
- iMac (Early 2001)
- iMac (Summer 2001)
- iMac (Flat Panel)
- iMac (17-inch Flat Panel)
- Power Mac G4 (AGP)
- Power Mac G4 Cube
- Power Mac G4 (Gigabit Ethernet)
- Power Mac G4 (Digital Audio)
- Power Mac G4 (QuickSilver)
- Power Mac G4 (QuickSilver 2002)
- Power Mac G4 (Mirrored Drive Doors)
- PowerBook G3 (FireWire)
- PowerBook G4
- PowerBook G4 (Gigabit Ethernet)
- PowerBook G4 (DVI)
- PowerBook G4 (1 GHz/867 MHz)
Notes:
1. The parenthetical product names iMac (Summer 2000) and iMac (Summer 2001) refer to the summer of the northern hemisphere.
2. A low-cost variant of the iMac (Summer 2000) model computer does not have an AirPort Card slot and thus cannot accept the AirPort Card.
AirPort Extreme Card

Figure 2
When sold separately, the AirPort Extreme Card (Figure 2) requires one of these computers:
- Power Mac G4 (FW 800)
- PowerBook G4 (12-inch)
- PowerBook G4 (12-inch DVI)
- PowerBook G4 (15-inch FW800)
- iMac (17-inch 1GHz)
- eMac (ATI Graphics) (See Note)
These computers always come with the AirPort Extreme card built in:
- PowerBook G4 (17-inch)
- PowerBook G4 (17-inch 1.33GHz)