Notebook "link to...failed"

OK, I've got an Acer1363Lci Notebook, and the Onboard modem is bad (doesn't handshake).  So, I tried adding a brand new Zonet ZFM5600 PCMCIA card (2 different ones), and neither will handshake properly, and if they do complete the handshake, which has only happened twice, it disconnects shortly after connecting.  The next thing tried was an old Xircom CEM33 modem/ethernet combo card, which didn't work at all (it could have been broken).  I then tried a Creative Modem Blaster v.92 USB, and it connects most of the time, but drops the connection within about 20 minutes.  I have been trying with both an earthlink.net dial up account, as well as a tried and true local Valuelinx account, which I know works because I use it for testing.  The PC has a fresh install of  Windows XP, dual booting with MEPIS linux (which I don't think should matter).  I can re-install windows if it would help.  Any ideas on fixing or on troubleshooting?

The errors are something like "the remote computer is not responding", or when disconnecting me, "Link to...failed."
When trying earthlink, it says the PPP handshake between the me and the remote computer were not the same, or could not connect.