E2000 slow in wireless mode

Question

I have a 30mbps connection.  Two desktops are connected wired and get 30mbps of download speed.
I have one laptop with Vista and only gets 16mbps while wireless and is only 20 feet away.
I have one desktop with XP sp3 with and D-Link WDA-1320 adapter and only get 6mbps in wireless mode.
What can I do to increase my wireless speed?
Thanks

Answer 1

Thanks for your help Dibbler.
After those adjustements, it is worse; 13mbps on the laptop and 5 on the desktop.
I'll tell you the whole story, maybe it will help you out in helping me.
I bought my E2000 in September, installed it had to call customer services for the final tweaks.  Then it worked great until last week.  I had 24-26mbps speed on my laptop and desktop.  Last week I noticed a drop in speed on the wireless side.  I called in customer service, after half an hour the tech person told me the router was defective, I was able to return it to the store for an exchange.  Brought the new one and try installing it with Cisco connect.  I could not, the system was telling me that it could not find the router.  Contacted customer service.  We were able to bypass the access to the router with the 192.168.1.1 address.  We tweak some parameters with no luck.  Afetr an hour on the line I was fed up.  So here I am trying this again through a forum.
Any other advice or adjustments you may suggest?
Thanks for your help.
Alain
(Mod note: Edited for guideline compliance.)