Strange dial-up behavior (WinXP)

It’s been happening consistently of late. I’m running WinXP Pro. I invoke a dial-up connection to the internet, and this works as expected: a small box appears noting that my computer is connected.

But when I start InternetExplorer or my e-mail client (Eudora), there is a delay of 1 to 5 minutes (!) before the program actually starts. After this long delay, all is normal. Usually, such a delay will not recur unless the computer is re-booted. No such delay is seen with an internet connection through a hub.

Does anyone have experience of this, or know what might be behind it?