While doing so I did find advise on a thing to do when NTLDR won't load on start-up - basically boot with the Windows CD/DVD, copy the files NTLDR and NTDETECT.COM from the CD to C:\, and then reboot. However, my computer won't let me copy NTLDR and NTDETECT.COM over, and it also refuses to let me delete the existing NTLDR and NTDETECT.COM on C:\, and it refuses to let me change attributes on said files, too - the administartor account apparently doesn't have access to do that. Hmph.
Anyway - while online two days ago, I did order new harddrives, just in case, and they should arrive today or tomorrow. Once they arrive, I'll take out the offending harddrive, install a clean install of XP SP3 on one of the new ones, and hook the old one back up to copy off it any files I might need/want. Hopefully I should be online again in just a few days.