Windows XP Install With Retail CD And OEM Product Key

I could really use a hand with an XP install I'm trying to do for someone. I've been reading for hours on this forum and others and can't seem to grasp what step I should take next. This forum in particular seems to be full of XP experts and has posts more recent than 2008, so I'm hoping I can find some help here.

Here's where I'm at right now:

I'm working on a Sony Vaio VGC-RB30 that came pre-installed with a copy of Windows XP Home Edition (I am unsure of the original service pack or if SP updates had been installed over the years). I do not have recovery discs, the OEM disc, or much of anything really.

I downloading the Retail SP 3 copy of XP that was recommended on the "Windows XP Repository" sticky on this forum, burned it onto a disc and did a format and reinstall on the OS partition (I believe the previous OS had a rootkit on it so I took the most extreme measure I could without purchasing a new drive).

Now, many of you are already saying, "Well that won't work you idiot," and you'd be right. I can't get past the Product Key input prompt in the installation process with the OEM key on the COA.

I would prefer to create a Generic OEM disc so I can reformat the drive and reinstall again (and have the disc in the future in case I need to do this again for someone else), but I can't seem to find a tutorial on altering a retail image in that way. At this point, I'd settle on having XP just running and activated. A step by step outline would be appreciated.

I've read about the unattended.txt and the winnt.sif and can't discern if using one of these and reburning the disc will circumvent my issue.

I'm currently on a Macbook with a Windows 7 VM installed on it.

Thanks all. Cheers.