I have tried many modem tweaking programs most of them arent worth squat. the one I have found that seems to ofer the best tweaking is called Throttle. get it and try it for the trial period if you like it then buy it. ( it is only 16.00) you can find it at majorgeeks.com
but relaisticly dont expect any guide or program to make your 56K dial up play online games smoothly it just isnt going to happen .