This paper studies the V-BLAST detection in a general multiuser space-time wireless system, in which each user's data stream is either (orthogonal) space-time block coded (OSTBC) for transmit diversity or spatially multiplexed (SM) for high spectral efficiency. The motivation behind this work is that each user adopting a signaling scheme better matched to his own channel condition proves to improve the individual link performance but the resultant co-channel interference mitigation problem is scarcely addressed thus far. By exploiting the algebraic structure of orthogonal code, it is shown that the V-BLAST detector in the considered dual-signaling environment allows for an attractive group-wise implementation: at each iteration a group of symbols, transmitted either from an OSTBC station or from an antenna of an SM terminal, are jointly detected. The group detection property, resulting uniquely from the use of orthogonal codes, potentially improves the dual-mode signal separation efficiency, especially when the OSTBC terminals are dense in the cell. The imbedded structure of the channel matrix is also exploited for deriving a computationally efficient detector implementation. Flop count evaluations and numerical examples are used for illustrating the performance of the proposed V-BLAST based solution.