Are you running wireless or are we talking a wired router?
Wireless 802.11n would be faster than wireless 802.11g from wireless access point to card but it won't speed up your providers connection per say.
What brand/model router are you using?
Feel free to hit me up on AIM at elijahmadmedoit if you need more info, I work in the industry.
Added----
If you need major a speed boost you could also buy a dual router that takes 2 cable modem inputs and bridges the connections for speed as well as redundancy should one connection drop.