Prey Veng is with 90km distance to Phnom Penh not far away (to the east). Kampong Cham is even closer with 78km to the North. Due to the former, bad condition of NH No 11 the place used to seem a world away. For good the government comprehensively overhauled the road in 2003 and now the city of Prey Veng is easily to enter.
There is lot's of minibuses going almost everytime of the day from Phnom Penh to Prey Veng (6000Riel). Most of them leave near the central market (Southwest corner), where you can also find lots of usual buses heading to Vietnam or Svay Rieng Province (they have to pass Prey Veng). Going with a share taxi won't cost you so much time to reach, but a little more money (8000-10000Riel, 2 hours). If you would like to go to Kampong Cham, there are also minibuses leaving from the centre of Prey Veng city for a 1 1/2 hour ride costing 4000-6000Riels.
The wonderful newly overhauled road is a mixed blessing for motorbikers as it gets a lot faster to Prey Veng, but less interesting and enjoying than the crappy, bumpier roads of old.