BleepingComputer.com: unable to connect using dialup

Dear Friends,
I just loaded a fresh XP OS on my dell dimension 3000 (not the Dell factory software, but a downloaded version which includes SP3). I'm trying to get it to connect via dialup, but keep getting "error code 678" saying "the remote computer did not respond". I am using an intel® 537ep v9x df pci modem. The modem dials and I can hear the data stream, but after nearly a minute it times out with the error code 678.
I am certain of the access number and the login information. I even had a tech at my isp walk me through configuration just to make sure I wasn't missing anything. Some of the various search hits mention the possibility of init string problems or other driver issues, but I am simply not knowledgable enough to narrow it down. I've tried disabling the network connection, reinstalling the drivers - I've even tried different modems, all with the same error code 678. Still, all of them dial, and you can hear the remote computer as well. I'd really appreciate some help here.

Sincerely,

Brian