I don't have this problem but I understand it may be related to a change in the Wi-Fi Power Saving mode in OS2008. By default it is now quite aggressive about turning the radio off to save power. It seems to cause problems with some wireless routers.

You can find the setting in the Advanced /Other section of your WLAN connection settings. Try turning Power Saving off and if that fixes it then you can try Intermediate to see if it is a usable compromise.