Try ipconfig /release , then do an ipconfig /renew . I say this because there have been times where just 'renew' didn't cut it for some odd reason and I had to release first.
Like others have suggested try setting it to static values to see if that works at all & definitely make sure MAC filtering isn't on. Make sure you have enough addresses in your DHCP pool as well.
I personally would go ahead and right away answer the question of whether or not the wired connection is able to get an IP from this DHCP server at all to immediately rule out any general network/OS issues and narrow it down to just the wireless adapter. Also make sure you're able to get an IP on a different wifi network to truly determine whether it's the AP or the laptop itself. At least then you'd know where not to look most likely.
Another thing you can try is taking all security off the AP and see if it connects at all.
If you haven't tried the driver from the OEM install or the manufacturer's website then I'd do that as well instead of using the W7 default driver for it. Try the Vista driver if none for 7.
See if wifi works with a Linux LiveCD such as one from Fedora or Ubuntu. Preferrably a 64-bit one.
On Dell Latitude XT2 Tablet PCs at my work The Dell Wifi had like 6 components that had to be installed for it, it's ridiculous. But our 2 XT's with Intel Wifi only require 1 component. Maybe you're missing something like this.
If the OEM OS was 64-bit then maybe see if you can extract the driver from it to try out.
Turn off the Windows Firewall just to see.
I'm not sure if Tomato firmware lets u do this but reserve an IP for your laptop's MAC on the Router so it will go into the list of knowns & maybe magically get an IP.