bad connection w/ router

I am currently using 8mbps cable modemhttp://www.arrisi.com/product_catalog/listers/index.asp?id=385 and D-Link DGL-4500 802.11n draft routerhttp://games.dlink.com/products/resource.asp?pid=643&rid=2373&sec=4. I have a 100mW amp. Buy Wireless antenna,WiFi Antenna,2.4Ghz 5Ghz Wlan Antenna,RF connector,RF pigtail cable,Lightning Protector,802.11 a/b/g, Omni ,panel ,yagi ,Grid antenna
and I can pick up my signal farther than I can access internet. Whats the deal? Using a 802.11g or 802.11n network adapter I can pick up my signal @ Very Good to Good but can't access the internet. As soon as I get 10' closer and do a speed test I'm screaming @ at least 5000 to 6000 kbps down and 1500 to 2000 kbps. up load. 10 to 15' further, nothing?

Move the router off the floor and away from walls and metal objects (such as metal file cabinets).

Metal, walls, and floors will interfere with your router's wireless signals. The closer your router is to these obstructions, the more severe the interference, and the weaker your connection will be.

Link : Wifi pune, Wi-fi Pune, Pune Unwire - 10 tips for improving your wireless network