Well, first things first, make sure that the wireless adapter shows up in Device Manager. If Windows 7 doesn't know there's a wireless adapter installed, you won't be able to use it.
If it's there, see if the caution symbol (yellow triangle with "!") is showing next to it. That would be a sign that the driver didn't install correctly: either the old XP driver doesn't work with Windows 7, or the driver didn't come with Windows 7. Either way, make sure you have the latest Windows 7 driver downloaded, either from the Toshiba website (preferably) or the actual adapter manufacturer's website.
If the adapter is installed & the driver is installed, but you still can't connect, make sure that it's detecting the available Wi-Fi. You may have to reenter the Wi-Fi password just to make sure it's saved correctly.