can’t connect win9x to NT – what is IPC$

Sometimes when I try to access a PC with NT4 installed on it from the PC with Win98
installed, I get the following message:

You must supply a password to make this connection:

Resource: \\some-name\IPC$

Password: _______________

And, no matter what the password is I can’t access that computer. Even if I was
logged in win98 as an administrator.

When I try to do the same from a NT4, I get the familiar “connect as:” dialogue box
and I have no trouble accessing the other computer.

What is exactly IPC$ anyway? I tried to find the answer in various books, with no luck.

Thanks