I have a Dell Optiplex G110 machine running NT and it has an MDP3858-W internal modem (fitted from new but never used). I havent been able to get the modem to work but it will dial up using an external modem & log on to the internet ok. I have downloaded the driver from the Dell website but when running the setup.exe (modem board wizard) it goes right throu the setup but on the last window it comes up & says driver cannot be installed. Hope this makes sense and appreciate any assistance!

just rephrasing..."I havent been able to get the modem to work but the computer will dial up with an external modem"....just for clarification

Hi Dave,
make sure, it's really the WinNT driver you have downloaded. You maybe should uninstall the external modem before trying to install the internal one, cause if your box is kinda stuffed with lots of devices there might be a resource problem (IR, I/O). Check your hardware devices for any problems (you find it in controlpanel). Make sure, you got the driver software for the external modem in case you will not succeed installing the internal one, so you can reinstall it without problems (remember, you don't have Internet access after uninstalling it). Save your configuration before making any changes to it (the rdisk thing, you know). Log in as administrator when you intend to install any hardware. Finally, if you can't get it working, Dell has a pretty good customer-support, I heard, you should have a customer-nr. that will help you on their website.
Good luck, Carl.