This computer ran Vista successfully for over a year. I reformatted the drive and tried to install XP.
The XP install took over 24 hours. It paused at 34 minutes probing devices. After some troubleshooting, I finally just let it be and it finished up the next day (!).
This happened with both XP and XP/64. I ended up with XP/64. Vista does not have this behavior. I tried pulling all removable devices and disabling everything in the BIOS with no effect.
So, fine, the OS is installed now and when it's up, it's very fast.
But XP now takes 8 minutes to boot up, I assume in probing devices. When I run it with the /SOS option, I can see the device drivers load, then it stops at this screen for 8 minutes:
The next step after the 8 minutes is chkdsk. I verified this by running chkdsk /f and rebooting.
I had same issue. It was an external drive that was hanging my boot. turnd it off, rebooted and went right into windows. Turned drive back on and all is well. Hope this helps.