Desktop/modem problem

[vin17]

I have an older T1800 series piece of junk eMachines desktop w/ XP Home SP2 and a 3+ year old DSL modem.

-I do a (destructive) reformat of my computer.
-I attempt to install my DSL modem's software.
-Towards the end of the installation a dialog box saying 'Updates for your modem are available. Would you like to install them?' After I click yes and it installs the batch of updates, again it reappears.
-It keeps reappearing (and I keep installing them) until eventually I get a Windows message saying '(The modem's program) has encountered an error and needs to close.'
-I try restarting the computer only to find the desktop loads for one second then disappears permantently.

Note: Before the reformat, when the computer was running *mostly fine*, I would get the same message. As well, I didn't have the modem's software installed and was instead using an older wired DLink router with minimal problems. The problem is that I am trying to install a wireless router but I can't get the internet to work properly with just a modem----PC connection.

So, does my modem likely have to be replaced? Fwiw, I just added 500mb of RAM to the original 250.

Thanks.