Encryption

I am looking at "Advanced Encryption Packpage 2007: Pro 4.5.7" available at
http://www.download.com/Advanced-Enc...?tag=emailThis

Here's my question. I will buy an XPS with Visa in January. I have an XPS at
my office purchased earlier this year that has XP Pro. I also have a
Latitude D810 with Xp Pro. And I use Lexar's Lightning (Pro?) 2.0 (or 2 mg)
memory stick to transfer files between them.

If I purchase this encryption software will it even keeps the files
encrypted since I copy some of them to one or more of the computers every
week? And will adding Vista to the mix complicate things.

Thanks.