Wireless internet dies every few minutes.

Hello. I'm using windows XP, on a slightly ancient computer, routing wireless with a D-Link Air DWL-122 USB device. About a week ago, the home modem (which my computer, obviously, is not attached to via Ethernet) completely died. A new one was sent and installed last night. I put in all the correct codes and such, and I should be able to get near-flawless wireless connection, as I was able to with the old modem. Same router, by the way. However, with the new modem, I can never connect fully except maybe for about two minutes out of an hour, and, as I'm typing this, I'm technically "not connected," although I seem to be able to access the internet. However, every three to five minutes, I lose even that connection entirely and I have to restart the connection and repair it. This sort-of fixes the connection…for three to five minutes. Restarting the computer has done no help, nor has uninstalling/reinstalling the router. As far as I am able to tell, I have everything set up properly: firewall is turned on and up-to-date, router is functional. I'm just unable to keep a decent connection for more than a few minutes. If anyone has any suggestions, I'd appreciate it a lot. I'd also appreciate it if you put it in layman's terms for me–I'm reasonably intelligent, but also reasonably hardware-dumb. If there's anything I left out in the description, please inform me. Thank you for your time.

A new one was sent and installed last night.
I put in all the correct codes and such,

Does that include all the steps required by your ISP, including:
ISP Username
ISP Password
DSL Modem Modem Access Code <– this is very important
____________________

If the above is complet….
then connect the DSL Modem out-put to the Router WAN socket
and connect a computer to one of the router LAN ports to set up the router.
Be sure you have Wireless Broadcast "turned on"
Write down the exact encryption code information for later use.

Using that same ethernet connected machine, us the XP Network Setup Wizard to Create a Home Network.
follow the on-screen prompts, including… create a network setup disk (save to floppy, CD or USB device)

Be sure that the "Wireless" switch is turned on on your laptop (not always one available, but if it's there it is usually on the front of the laptop and causes an LED light to come on)
Be sure your Wireless Adapter Driver is functioning properly

Run the network setup disk on your laptop. (this "should" cause all machines to be in the same workgroup and all to have the same encryption code)

You "may" still have to enter the encryption code information when checking for available wireless networks and connecting to your own.

Be sure you are trying to connect to your own and not the neighbors' connection. (you should select a Name for your Router that is easily identifiable, but different from others in your neighborhood. (for instance, do not select "D-link router" as your router name.
Instead select something like RoadToAnywhere.

Best Regards