Trouble connecting to my router with my DS

I've had my ds for just over a year now and I'm still unable to connect to the internet with it.
I have all of the stuff you need including a wireless router (which says it is unsecured)
I was wondering what would cause bthis problem in connecting, I have contemplated buying the wireless USB from nintendo but have decided to seek advice before making that investment

Thanks in advance

I've found that the DHCP client on the DS just sucks beyond belief

If you manually enter in the correct network information, it should work (as long as when you scan for AP's you can see the router)