The said official weigh-in for the TUF 11 MMA event will be in the Key West Ballroom at The Palms. It is free and open to the public.
However, if it is not possible for you to visit the weigh-in in person, then you can watch the said event LIVE and FREE online at 7pm ET/4 pm PT including UFC.COM/live, UFC BACKSTAGE CAMS, UFCFIGHTCLUB.COM (members only) MMA Fanhouse and Yahoo!Sports.
These streams mentioned on the sites are free-of-charge and can be used in Macs or PCs. Just make sure that you have the appropriate Microsoft Silverlight plug-in watch the official weigh-in.