Upgrading my System

I recently upgraded my Dell Dimension 8400 to a more power ful Dimension 9100. The systems are similar but ofcourse the 9100 is powerful, and a slightly different motherboard and processor architecture.

Like usual i unpluged my hard drive and moved it over to the new machine, on power up Windows XP asked for new drivers e.t.c.

The problem is that something has not upgraded or is running the wrong driver as the machine is running slower, especially in games.

The specification of the 9100 should run almost any game in full power, but becomes slow and jurky.

How can i either make Windows XP reinstall all drivers or find the problem?

The graphics cards are the same, so i am pointing it to either the processor or motherboard drivers.