I used "Data Rescue 3" to recover a folder full of files called login-00001.keychain (to 587). How do I join them?
The system will create a new login keychain the next time you log in. You will have to re-enter passwords for email accounts, wifi networks, etc., but in general loss of the keychain file isn't too traumatic assuming you have a list of your passwords stored securely elsewhere. This may not be so trivial if your keychain contained security certificates issued by your company or institution. If that may be the case, call IT.
FWIW, I suspect that the multiple recovered files reflect multiple copies (or portions of same) reflecting various versions of the keychain as it was modified. I don't believe they're disjointed fragments that need to be combined. If anything, I'd try renaming the latest file (by date) and if Keychain Access opens it, run Keychain Repair (First Aid?) against the file. But I personally wouldn't bother. (You can give the file a temporary name like "recovered" for testing purposes, then rename it if you decide to use it--or just copy its contents into a newly created login keychain.)