For what it is worth, I've used Crypt::RC4, Crypt::Solitaire (which implements the Pontifex cipher from Cryptonomicon), Crypt::Rijndael_PP, and Crypt::Blowfish_PP all on my HP Jornada. Not an ipaq, I know, but both run Windows CE, so I would think that if it works on the Jornada it'll work on the Ipaq. There is a LOT of crunching that goes on with both Crypt::Blowfish_PP and Crypt::Rijndael_PP, so performance suffers a bit.
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Kurt