Well first of all, your internet speed has nothing to do with it. 802.11G is the protocol used by your wireless network...it means a lot of different things but the most important is the speed of the network which is 54Mbps.

If you have an antena on the card that's nice, make sure it's attached properly or it's just as if you don't have any. The important part beside the card is the router...that's the box which is connected to your modem which provide the Internet connection.

When the connection is initialized you should see two computers near the clock of your computer (bottom-right) if you double click you on those you should get a popup regarding your Wireless connection status...there you will see the signal strenght. If it's low the speed will drop to compensate...however if it's not good at all there's a good chance that your connection will drop and come back again.

Here's some info required so that most of us can help you.

Which Operating system? (Windows 98, 2000, XP, GNU/Linux, etc.)
What brand or router/wireless card (Linksys, d-link, etc.)
How is your computer located regarding the router? (upstair to downstair, on the other side of a 3 feet thick cement wall. All those things affect signal quality.

Also just to make sure, are you absolutely sure that it was your Wireless connection that failed? Does it happen frequently. It could have been the poker client, the router itself or your modem.