D-link Speed Problems

I installed D-link wireless system for my computers about 3 weeks ago. I uses the following pieces:
router- DI-524
Wireless Card for notebook- DWL-G630
Wireless PCI adapter- DWL-G510

When I first instlled it, the computers both went very quickly, that lasted about 3 days. Now they are so slow that I can't hardly get on the internet homepage, let alone get anywhere, pages take 15 minutes to partially load. But sometimes it's really fast.

Any ideas on how I can fix this.

 

When you go into your wireless settungs try disabling any authentication settings and make sure windows firewall is off.