if your running cf and cant run php then how are you running vb on the server. you may have to recode the way vb uses the password to conform with cf standards (i dont know cf at all)
But CF encrypts stuff in a 32bit format, PHP does it differently.
vBulletin does not encrypt anything. The only information it doesn't preserve as plain text is the password, and that is hashed, not encrypted, using the MD5 algorithm: http://www.php.net/md5 . Virtually any language will have MD5 hashing functionality.
Encryption is two-way: text can be encrypted and then converted back to the original text. Hashing is one-way: the hashed text cannot be converted back to the original text because information is lost in the process. This has the disadvantage that two strings can create the same hash, but the chance of that happening is ridiculously low, something like one out of 16^16.