"but for some reason I cannot get to my original C drive from my XP boot"
Do you mean from your 7 boot?
If you cannot see a drive/partition, from Windows 7, you will need to mount it. This will probably be sorted with the final release. I have found that if you run the 7 install disk from within Vista/XP, it will automatically mount the other OS from which you installed. However, do this:
Open the Administrative Tools - Computer Management - Disk management.
In there, you should find that you can see all the disks and partitions, but they may not have a letter designator. By right clicking them, you can assign a letter and you will then be able to see them in, for example, Windows explorer. You can juggle the letters around by changing and reassigning, but it would be a bit of a pain.