In this paper we present a new implementation of the distributed Lagrange multiplier/fictitious domain (DLM) method by making some modifications over the original algorithm for the Newtonian case developed by Glowinski et al. [Int. J. Multiphase Flow 25 (1999) 755], and its extended version for the viscoelastic case by Singh et al. [J. Non-Newtonian Fluid Mech. 91 (2000) 165]. The key modification is to replace a finite-element triangulation for the velocity and a "staggered" (twice coarser) triangulation for the pressure with a rectangular discretization for the velocity and the pressure. The sedimentation of a single circular particle in a Newtonian fluid at different Reynolds numbers, sedimentation of particles in the Oldroyd-B fluid, and lateral migration of a single particle in a Poiseuille flow of a Newtonian fluid are numerically simulated with our code. The results show that the new implementation can give a more accurate prediction of the motion of particles compared to the previous DLM codes and even the boundary-fitted methods in some cases. The centering of a particle and the well-organized Karman vortex street are observed at high Reynolds numbers in our simulation of a particle sedimenting in a Newtonian fluid. Both results obtained using the DLM method and the spectral element method reveal that the direct contribution of the viscoelastic normal stress to the force on a particle in the Oldroyd-B fluid is very important.