If you are experiencing slow download times, or are receiving errors while connecting, check the following:
Check the location of your router. Move your router away from walls and off the floor and try to place it in a central location in your home. Also, keep it away from metal objects such as metal filing cabinets which can cause interference.
Check for interference.
There are two types of interference that can cause problems with your wireless connection: Wireless interference from other wireless routers in your area. Did you see several network names (SSIDs) come up when you used Search for an Access Point? This could indicate a lot of WiFi activity in your vicinity that can cause interference.
'Noise' from cordless devices (cordless phones), or wireless electronics (wireless keyboards, headphones, cell phones), especially those using the 2.4GHz frequency, can interfere with your wireless signal. In addition, older microwave models can cause wireless interference.
To minimise interference try the following:
Do not use other wireless/cordless devices when trying to get online with your Wii console. Also, avoid electronics that use the 2.4GHz frequency, instead look for devices that use the 5.8GHz or 900MHz frequencies.
Change the channel on your router. By default most routers broadcast on channel 6. Change the channel setting to 1 or 11, as those do not overlap with other channels. Router "Channel" settings are typically found in the "Wireless Settings" area of your wireless router's setup utility.
Upgrade to a hi-gain antenna, and/or add a wireless repeater. If your wireless network signal is weak, you can add a hi-gain antenna that focuses the signal into one direction. This allows you to aim the signal directly in the direction of the Wii. A wireless repeater extends the wireless range. Both devices can boost your signal strength and allow the signal to cut through interference and noise more effectively. Most retailers that sell wireless routers will also have these accessories available.
Upgrade 802.11b devices to 802.11g. While 802.11b is the most common type of wireless network, the 802.11g network is about 5 times faster. Most 802.11g routers are backward-compatible with 802.11b, so you can still use any 802.11b devices that you currently have.