I feel your pain in regards to this router. I use to use it and it was plain crap, needing a reset every 15 to 20 minutes.
I did find a solution, and that is to change the firmware to a different model of the dlink firmware (it supports this router). This fixed ALL issues in regards to this router. If you are doing this process, make sure you do it over a wired ethernet connection, and not via wireless.
Here is a link with more information.
http://www.dslreports.com/forum/remark,15995077
Note, i think this only works with Rev A of the router...(At least I can confirm it works with Rev A)
PM me if you have any q's.