Actually, "/home/tchuserid/mail/" is exactly how I had it set up, and it gave me errors. Perhaps, as you said, it had to do with the fact that INBOX.Sent, etc. already existed. However, having removed the path and left it as "" I can now access Squirrelmail and my mail appears to be there. Checking my files, it doesn't look like INBOX.sent was recreated in another location, but I could be wrong.
You know, now that I think about it, I wonder if Cpanel Squirrelmail created those files in /home/tchuserid/mail/? Are they used by popmail at all? Or are they a webmail thing? Maybe I could delete them and then my new Squirrelmail install can re-create them?
Is there any security risk to having 777'd my data and attachments folders if they are sitting in my home folder?