Can I use my ATT air card with my Toshiba Portege M200 tablet pc?

I have owned several tablet PC's and all of them (including my most recent Toshiba) worked just fine with the existing wi-fi card. Please be clear, however, that AT&T wireless air card service and "wi-fi" are two different things.
Your AT&T card pulls internet service over cellular connections, and your wi-fi card connects to a local hot spot (if available) or your own wireless internet access.
First of all, be sure that you have an active AT&T laptop connect account and then follow these steps:
Power on your laptop. Insert the AT&T wireless air card into an available USB slot. Wait a few moments (this may take several minutes some times), and the card will typically start attempting to install itself and its software. If you have any trouble with this, ATT provides free installation tech-support at the following site:
http://www.wireless.att.com/businesscenter/solutions/wireless-laptop/modem-cards.jsp

You may also have them contact you at your convenience by going to this page and filling out the form:
https://www.wireless.att.com/businesscenter/b2b/contact_us.jsp?wtLinkName=ContactATT&wtLinkLoc=RN

Hope this helps!
Jeff