Best and easy method, is buy Acronis Disc Director Suit 10. It is easy to reduce the partion size with it so that the drive leaves free sapace that you can create a NTFS partition for XP. The above Program also as a Dual boot mager with it. I use it to dual boot 98se and XP on different drives. It as all the tools you need to do the job easy
"Whats the best way to obtain the motherboard drivers?"
Normally a new system should come with a CD for the motherboard. Otherwise from the website of the motherboard manufacturer.
"Are they accessible through Linux?"
No - it works ion an entirely different way.
If Linux is no longer wanted (can't understand why - but that's your friends choice - have they actually tried using Linux?) - then follow the advice of Diodorus Siculus. You don't need any other software other than the XP CD.