There are Linux distros that are aimed at Intel/Marvell PXA series processors, but I'm not sure a proper desktop would work in the relatively low 64MB of RAM the Dells have, so a major distro like ubuntu may not work well if at all on the current crop of PDA processors. There is a current project (on the back burner) to get Linux on the Dell line, but that has been underway for awhile.
X5/X3:
Handhelds.org - Linux on Dell Axim X5
X30:
Handhelds.org - Linux on Dell Axim X30
X50:
DellAximX50 - Handhelds.org MoinMoin Wiki
Other sources/articles:
Dell Axim X50 embraces Linux - MobileRead Forums
Slashdot | Dell Axim X50 Running Linux
Familiar Linux (Ipaq) project:
the Familiar Project
p.s. I do have Ubuntu on my dekstop, and I'm trying to get it running on my new laptab. Got a dual-boot with SUSE and Vista(blech) home ultimate now. Okay, I actually broke the SUSE... gonna reinstall once I get Ubu working.
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