Wow, I'm surprised at the abundance of responses!
Does it seem to start OK if you start in Safe Mode? Possibly some driver is misbehaving while loading.
Are you showing any consistent errors in the Event Viewer?
Safe mode didn't take off; stalled on a file. I'm not familiar/savvy enough to really make heads or tails of event viewer, there's so much data displayed there and I'm not sure what I'm looking for.
It certainly sounds like that what's going on. Check your C: drive and see if you still have any partitions. If so, is it a partition with xp on it. If it is, then format partition and then reallocate it back to your C: drive.
There's a Window.old there with nothing in it but an autoexec file and config sys.
There's also a D: drive on this computer with what
appears to be Windows XP and all the files I loaded onto it while I was attempting to make it work with XP. I'm guessing this is the huge "duh" sign I'm looking for, but obviously I'm hesitant to just go and format the thing because A) I don't know if what programs/whatever I'll need to reconfigure from it first, if any, and B) I don't want this to end up with me formatting my valuable information by having to perform a reinstallation Windows 7.
Oh, to address something
patcooke said, D: is listed as the Logical Drive. C: is displayed as the System, Boot, Page File, Active, Crash Dump, and Primary Partition.
Alternatively you could do a system repair with media installation disc.
I'd be happy to, if it won't clear off my current data and won't result in a weekend of reinstalling drivers and finding the product keys for every little thing.
I'm hoping the formatting of D is the simple answer I'm looking for..? Or possibly a change in configuration elsewhere, in the BIOS perhaps?