I think this problem might be caused by the router I'm using now, or maybe the ISP, because the same thing happened on the N900.

I used the App. manager on the N900 to install the Maemo PC Connectivity packages, but it was failing. The progression bar never changed and the installation was aborted after a while, and I could see the timeout messages on the App. manager log.

So, I used apt-get on an X Terminal with the same options (-o Acquire::http::Pipeline-Depth=4), and voilà! It worked!