Your Windows XP computer should not be in the DMZ unless there is a specific reason to do so unrelated to IPv6. If your goal is still to have the router be your IPv6 endpoint, the first thing I would do is remove the Windows XP machine from the DMZ and remove any configuration you did on the Windows XP box to try and obtain IPv6 connectivity other than installing the Microsoft IPv6 protocol stack, then reboot the XP machine. Since you're using radvd on the router, you will not need to make any configuration changes to either the XP machine or the laptop other than loading the Microsoft IPv6 protocol stack in order to obtain basic IPv6 connectivity.
I am more familiar with OpenWRT than I am DD-WRT, but here are some basic thoughts. It looks like br0 is your bridge which I presume is your lan and from the web site you copied instructions to create a new tunnel interface called he-ipv6. From the commands you entered you have created an IPv6 tunnel on he-ipv6 and assigned it an address of 2001:470:1f06:74d::2/64. Which is good. Have you added an ipv6 address to your br0 interface from your delegated /64 of 2001:470:1f07 ? If DD-WRT supports shell access or running commands, it would be helpful to see the results of the ifconfig from the router.
To answer your radvd question directly, you can use radvdump if installed on the router to see when radvd sends advertisements to the network. Radvd only sends announcements periodically, so it may take a while for one to show up. The format from the dump is similar to the configuration but also includes the default parameters. From the configuration you posted, I would remove the MTU entry and the Base6to4Interface entry which is for a 6to4 setup.