dads having internet problems, help me help him

[isuace]

My father is having some problems with his internet. He connects and according to him for the first minute or two it works ok. Then performance degrades to the point that he has to log off and log on again. He says that he has to do this several times before he can get it to work, if it will at all.
He has called his ISP and they keep telling him that it is because he is running win2k. They have no support for win2k at all, only win98.
I personally cant believe that they have no support for an OS that has been out for 4 years now and is widely used. I cant figure out what the problem is, they have convinced him that it is something wrong with this machine.
Does anyone have any ideas on what to try? I am at a total loss and he keeps coming to me over and over to "fix" his internet. Any ideas would be greatly appreciated.

[Byte 2.0]

that is so lame they don't support win 2k. heck, Microsoft has ended support for win95, and it getting close to ending support for win98.

I take it he is connecting over 56k modem?
what connection speed does he connect at?
also when it gets down to the very slow or stops, can he ping out?

I believe I woud look into another ISP if they can't ofter any ideas or any support for win2k.

[reboot]

What modem, chipset, and what driver version?

[isuace]

Thanks for the replies.
I am going to talk to him, hopefully tonight, and get some more info and report back.
Thanks