DDWRT is a custom Firmware for the WRT. While Gottago has a valid point, I have to disagree with using Cisico's firmware. Its junk on the WRT. The 3200 is kinda scetchy with DDWRT, so I would stay with Cisco's firware on that guy.
DDWRT has more features, a much more stable caching code and opens more options that aren't available with the stock firware. I.e. you can change RX/TX power, CPU speed, and actually add cache(hardware mod). Point is, this firmware is more stable than the original. The GUI is also way more friendly to noobies for setup.
All my multi router setups use different SSIDs, unless I'm strictly using DDWRT on both routers. Most of my customers I've set up in the exact same situation have different band/model/chipset routers. Its more reliable and easier on me and the customer to just use different SSIDs, on the same subnet. You just have to make sure you set your DHCP range above the second router so you don't end up with IP conflicts. I.e. first router LAN IP 192.168.1.1, second router LAN IP 192.168.1.2. Set the first router's DHCP to start at IP 192.168.1.3, second router DHCP set to off.
Again, I'm out of time to go into further detail. Most of the suggestions are actually viable solutions. However, you're usually limeted by firware and router options to do some of the suggestions.