I can't setup my D-link DIR-600 router to allow remote desktop access to a Win-based PC on my LAN.

I would contact your ISP for help with this one. It should work but you would want to check the LAN and WAN settings to make sure they work on the network since there have been changes.

Press and hold the RESET button at the back of the router with the power ON until the LEDs flash at the time the release the RESET button. (firmware version was 3.00, and upgraded to 3.05) Connect a LAN cable from the D-Link to your laptop/computer's LAN port, open the browser on your laptop/computer and enter the D-Link's configuration URL..
http://192.168.0.1
The default login = admin
The default PW = blank (just press Enter) You can now change the default admin password.
You can now configure the wireless settings. Now configure the wireless card in your computer/laptop with the router's wireless settings. To secure your wireless network from unauthorized access, please click on this link and follow my instructions :- http://www.fixya.com/support/r3559128-wireless_router_security

Unfortunately without a laptop or a desktop you cannot access the router.

Connect a LAN cable from the D-Link to your laptop/computer'sLAN port, open the browser on your laptop/computer and enter the D-Link'sconfiguration URL..
http://192.168.0.1
The default login = admin
The default PW = blank (just press Enter) You can now change the default admin password.
You can now configure the wireless settings. Now configure the wireless card in your computer/laptop withthe router's wireless settings.
To secure your wireless network from unauthorized access,please click on this link and follow my instructions :- http://www.fixya.com/support/r3559128-wireless_router_security

Connect a LAN cable from the D-Link to your laptop/computer'sLAN port, open the browser on your laptop/computer and enter the D-Link'sconfiguration URL..
http://192.168.0.1
The default login = admin
The default PW = blank (just press Enter) You can now change the default password.
You can now configure the wireless settings. Now configure the wireless card in your computer/laptop withthe router's wireless settings.
To secure your wireless network from unauthorized access,please click on this link and follow my instructions :- http://www.fixya.com/support/r3559128-wireless_router_security

Connect a LAN cable from the D-Link to your laptop/computer'sLAN port, open the browser on your laptop/computer and enter the D-Link'sconfiguration URL..
http://192.168.0.1
The default login = admin
The default PW = blank (just press Enter) You can now change the default password.
You can now configure the wireless settings. Now configure the wireless card in your computer/laptop withthe router's wireless settings. To secure your wireless network from unauthorized access,please click on this link and follow my instructions :- http://www.fixya.com/support/r3559128-wireless_router_security

Connect a LAN cable from the D-Link to your computer's LANport, open a browser and enter the D-Link's configuration URL. OR open thebrowser on your laptop and enter the D-Link's configuration URL..
http://192.168.0.1
The default login = admin
The default PW = blank (just press Enter)
You can now configure the wireless settings. To secure your wireless network from unauthorized access,please click on this link and follow my instructions :-http://www.fixya.com/support/r3559128-wireless_router_security

put another lan card in pc
share your connection using ICS from network properties from first one
put a straight cable from pc to router

give the gateway of router to laptop
remember!! the class of ip's should be the same

you are done

Ok...don't panic....take it all back out thru control panel>add/remove...reset your wimax modem by the little reset hole in the back as this can be an issue sometimes by adding the modem in the incorrect order. You should install everything but the "lan" cord from modem to modem last. A good test is to take the "lan" cord from your winmax modem and plug it right into your pc and you should have internet.

u have to setup the router in it's settings... by entering 192.168.0.1 into the browser and use username : admin ... without password