Problem with SELECT Statement

[Jamie Yane]

I am new to MySQL so I apologize in advance for my ignorance.

I have two tables say TableA and TableB. I want to be able to select
a group of entries from TableB but only display the records that meet
the search criteria and are NOT in TableA. For example.

TableA:
111,John,55
112,Joe,13
113,Matt,55
114,Shawn,55
115,Dave,13

TableB:
990,John,12345678
991,Joe,12345678
992,Matt,12345678
993,Shawn,87654321
994,Dave,87654321
995,Steve,12345678
996,Tom,12345678

I want to display a list of people from TableB belonging to group
12345678 who do not already appear in TableA's group 55. The result
should be

Joe
Steve
Tom

I have had no luck at all finding a solution. I know this would
probably be pretty simple if I were able to nest queries within
queries but the version of MySQL we are using doesn't support this.
Any help would be greatly appreciated.

Thanks,

Jamie