On my Ubuntu 7.10, I built gdb 6.7.1 and the programs are correctly stopped with it. This version of gdb works fine, finaly. So, what is the problem?
Please try to launch your program in gdb in a terminal then enter:
Qt Code: 
  1. break main.cpp:8
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then run it.
8 is the line number in the main function, change it if the line 8 doesn't exists. You have added the breakpoint in the same way that is made in qdevelop. Say me the results, please.