Retaining walls really require a drain tile installed behind them and also lots of gravel. This allows the water to drain off which prevents the hydrostatic pressure from toppling them over. You could try to anchor the ones you have but if they're really leaning forward then it may be best to rebuild them the right way. There are lots of interlocking cement blocks you can get nowadays that'll allow you to DIY but you'll need to make sure you install the appropriate drainage to prevent it from happening again. Below are a few links with lots of info on them, hopefully they'll help you out some. And let us know if you need anymore help.
http://www.thisoldhouse.com/toh/know...681-8,00.html#
http://www.extremehowto.com/xh/artic...ticle_id=60276
http://www.askthebuilder.com/RetainingWalls.shtml