Yeah, but the freeware versions do not have PGP Disk in them. They're only for encrypting individual files.
To understand how it works, the basics, I STRONGLY recommend you download V2.6.3i at
http://www.pgpi.org/products/pgp/versions/freeware/dos/
and that you read the tutorials.
Skip everything that pertains to program usage, the command line interface commands and switches, etc but read the broad principles and explanations of how the program works.
The help files of hte new programs are aiming at functionality, but this is TREACHEROUS for it can lead you to use the program in an unsafe manner. Their interface is designed to be as dumb-proof as possible, but still, you can make major mistakes.
SECURITY IS NOT THE USAGE OF A TOOL
IT IS A SET OF STRICTLY ADHEREDED-TO PROCEDURES !
If you don't adhere strictly to procedures, you will put yourself to more risk than if you do not use encryption, for you will fall victim to a false sense of security
If you don't understand exactly how and why PGP works, DO NOT USE IT. That way, you won't commit to computer things that you do not want other people to know.
Only V8 runs on XP, and there is no free PGP Disk. I have a paid copy of V7 with PGP Disk and that's why I'm sticking to W2K.
There is a hack on V6 to have PGPDisk work on the freeware version, and I think it's available on PGPI.org site.
The difference between the US and international version has to do with patents, but most of them are expired or about to expire in the US anyway. The international version is reputed to be superior.
You can download the full source code to these programs, inspect the code for backdoors and compile them yourself if you're really of a suspicious nature...
You should never ever trust any encryption program for which the full source code is not published. The secret shall never be in the code but rather in the mathematics of the algorithm.
The last version of PGP does not have it's full source code published, AFAIK (things might have changed though).
The company changed hands several times. The original software was published as GNU Public Licence Freeware.
There is a long (10 years) story of that software.
A new version of the freeware, PGP compatible is being written: GPG. Last time I checked, it was still at the Linux-developper's level. Eventually, a full freeware, peer reviewed, will emerge from that but it will take some time (years).