My friend’s got a PC which seems to be on its way to being completely hosed, so I’m fixin’ to reformat her HD tonight and help her do a clean install of XP. Since I’m strictly a Mac user, I just want to make sure that I’m choosing the best options prior to and during the install process.

It’s a 2.5 ghz, Pentium 4 Sony Vaio desktop of some sort.

First of all, basic stuff:

What are the different ways of forcing this thing to use the Windows install CD as its boot drive? I know there are one or two obvious ways, but I know this also car vary from one PC to another.

Secondly:

Just in case there are any viruses hiding at some really deep level where most virus software can’t or won’t look, is there anything I should do at the BIOS level to make sure everything’s fresh and new?

Next:

When formatting the HD, what file system/format is the smartest one to choose?

Furthermore:

What options should I say "No" to during the XP install? If memory serves me correctly, it’s not like installing OS X where you have a fun ‘n’ easy interface that lets you leave out stuff you don’t need, such as foreign language libraries and drivers for printers you don’t own and Garage Band’s library* and whatnot. Is it possible to do a custom install, and if so, is it a good idea?

Lastly:

She’s entitled to a copy of XP, ’cause that’s what came with her computer when she bought it new. Naturally, she doesn’t recall whether she ever owned any system restore CDs or where they might be. Therefore, we’re using my copy of XP which, ahem, doesn’t ever need to be registered. However, since she [i]is[/i] entitled to full, legit status, is there a way to enter her PC’s serial number or something and have MS recognize that she’s fully on the up-and-up?

Like I said, this copy of XP will download and install MS updates just fine the way it is, but I figure, hypothetically, from a support standpoint, it can’t hurt for her computer to have all its ducks in a row. Is this possibly one instance where a person actually [i]would[/i] want to install and run the dreaded WGA? My every instinct says not to, but I figure if WGA’s whole purpose is to tell you how to make everything legit, and facilitate doing so, then it might possibly be of service in this case.

Thanks, as always, for your guidance in this matter!
*I’m pretty sure XP doesn’t include a Garage Band library.