Hey rcigliano...
What firmware are you running on your DIR-655? I have 1.11
Here is my setup (which is almost the same setup you have).
Dell Inspiron 1505 Notebook
DWA-643 Xtreme N Notebook ExpressCard
DIR-655 Xtreme N Gigabit Router
The router has the following setup
802.11 Mode : 802.11 Mixed N+G
WPA Mode : WPA2
Cipher Type : AES
Channel width: Auto 20/40 MHz
The wireless status page of my router is reporting
162Mbps and a signal of 100%
Dlink Wireless Manager is reporting 300 Mbps and a signal 100%
XP is reporting 300 Mbps
I believe all of them are correct. However, the wireless status page in the router is what the computer is actually using at that time.
I have done a test, opened up a bunch of youtube videos at the same time. And at the same time, transferred files from my computer to my NAS. I watched the speed in the router page go from 162 up to 300 as the bandwith usage increased.
This makes sense to me as the computer is reporting 300Mbps. But the router reports what it is using. Which is pretty cool!!!