Dell has some more documentation on the X51/X51v including the Owner's Manual.
http://support.dell.com/support/edoc...1/EN/index.htm
Owner's Manual
http://support.dell.com/support/edoc...m/NC341bk0.pdf
Added: From the Owner's Manual
Yes it will use WM 5.0, yes the High version has 256MB of Flash Memory
Using Microsoft® Windows Mobile™
Version 5.0 Software for Pocket PC
Premium Edition Mobile 5.0
The Windows Mobile 5.0 operating system comes with a host of new
features and interface improvements. The screen view and touchpad is
similar to Windows™ XP for computers. RAM is only used for running
applications. Flash ROM is where all application, PIM data, and file storage
happens. For details, visit the
www.microsoft.com website.
System Information
Processor
Hi Intel® XScale™ PXA270 processor at
up to 624 MHz
Med Intel® XScale™ PXA270 processor at
up to 520 MHz
Low Intel® XScale™ PXA270 processor at
up to 416 MHz
Memory
Hi 64 MB/256 MB NAND Flash ROM
Med 64 MB/128 MB NAND Flash ROM
Low 64 MB/128 MB NAND Flash ROM
Operating System Microsoft® Windows Mobile™ Version 5.0
software for Pocket PC Premium Edition