Boot process stops but then continues

Hello,
I am using Windows XP Professional, with SP3 and all the updates installed.
I am having a strange problem with the start of Windows. It boots normally,
but when the desktop and the wallpaper appear, there is a pause of about 30
seconds, in which there is no disk activity. After that pause, everything
boots normally.

I used Bootvis and BootLogXP to find out what processes could be causing
that pause, but I didn't find anything useful. Maybe I don't know what to
look for.

Anyway, I removed several unneeded services, even uninstalled antivirus
(Avira), and managed to cut down the boot time in 15-20 seconds. But the
strange pause is still there.

Any ideas on what should I try next?

Thank you.