This particular problem has hit me a few times, particularly with some ASUS laptops. You would set up the PC normally, and everything works fine. Then we go for the final reboot (it is always the last one that does it).
During the restart, we see the Windows Logo (XP or Vista), and the running bars underneath. Suddenly, everything goes really slowly, as though in slow motion, and it does this for about 30 minutes (I timed it once).
The problem lies in the memory effect on this particular network card. To solve this problem, ASUS tech support recommended the following steps.
1. Shut down the PC/Laptop.
2. Remove the battery, or disconnect it from mains power, and disengage the network cable.
3. Restart the PC, and update the network card with the following driver – http://dlsvr.asus.com/pub/ASUS/nb/M51E/LAN_XP_080407.zip