I bought a Lexar 512MB SD card and I can only install (hotsync) .prc files in it. But I need to copy some folders containing .dat files and I can't copy them in the SD card. I can use Palm Quick Install to add them in the expansion card but when I hotsync it says "There is no application on the organizer to handle this file (0x4005).

Is there any possible way I can copy these folders in the SD card either from Windows or Linux?

If you have a USB SD card reader/writer, you can remove the card from the Palm, put it in the reader and plug it into your Linux (or Windows) machine and write directly to it (it will look like a small disk drive to the system).

Alternatively, you can install a utility like CardExport on your Palm. When you run it, it makes the Palm act like an SD reader to Windows or Linux.

Personally, I prefer the stand-alone hardware reader (typically under $20), since it's not specific to the platform. That way, you can use it with the card in your digital camera, or Windows/Linux PDA if you ever change platforms.