[yongkimleng]

hmm.. dd-wrt, means you are using a v5 router which has only 8mb ram and 2mb flash?
You'd be better off with an older one which has more flash ..
But if you are thinking of serving a whole arena of users (probably > 250) I think you will be better off with a linux box giving out serving DHCP on class A or B subnets, with the router merely bridging your wireless and wired interfaces (i.e. disable internal dhcp).
The number of requests / flows may also be maxing out its ram.