He said, twice, that he had NOT encrypted them. I agree that it sounds like user error though, if they were stored on an NTFS volume, he would have had to take permission to access them once re-installing XP, and likewise, the filesystem is inaccessable to normal DOS.
My supposition that XP actually borked the NTFS filesystem in this case, may have been incorrect though, the OP probably just didn't know how to access them, as he claimed that he could see them (read directory), but was prevented from accessing the files' contents to copy over to another drive. However my suggestion to use FAT32, in case there is a need to access the filesystem from a DOS boot disk, is still a valid point.
Edit: I swear that I thought I had clearly read him stating that he had not encrypted them, but I guess perhaps I read it too quickly. I guess he was speaking of his second installation, and, reading between the lines, it is possibly to imply that he had encrypted the first installation. So I guess he didn't state it explicitly either way, and it is perhaps likely that he did encrypt the first installation. My apologies.