I didn't mention BIOS and doubt that you would have to make any changes in your system Basic Input Output System (BIOS) also referred to as CMOS or simply SETUP.
I have no idea what components your machine has, but the items you will most likely want to install are as follows:
XP Installation CD
then in the following order:
Motherboard Chipset Drivers
DirectX9.0c (from Microsoft downloads)
Any additional peripheral Device Drivers,
JAVA Runtime Environment 6 here: http://java.sun.com/javase/downloads/index.jsp
Firewall - I use Zone Alarm (free), but Sygate, Commodo, Kerio are all good (and free)
AntiVirus - I use AVG AntiVirus (free)
AntiSpyware - AVG AntiSpyware (free) and Spybot Search & Destroy (free)
____________
Burn the files to a CD for easy installation.
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If you have other Devices, like DVD (Power DVD or Interactual DVD) or CD-RW software like Nero or Roxio, then have the paid version CDs handy.
If you have Printer, download the appropriate drivers from the manufacturer's Website.
Some USB devices have their own software, for instance External Hard Drive.
Generally cameras, microphones, speakers, keyboards, mouse, all will function just fine with the drivers installed by XP.
Wait until you are online to get add-ons like Flash Player or Shockwave, or google toolbar.
You'll have to be more specific about your concerns, if you have devices beyond what I've listed above.
Best Regards
Edit:
EDIT: Do I need to download PCI drivers too?
What PCI Cards does this machine have?
Network Interface Card (NIC) ?
Sound Card ?
Graphics Adapter ?
Dial-up Modem ?
Others ?