PDA OS comparison

Feature/OS	Windows Mobile 2003	Palm OS 5
Multitasking	Yes	partially
16/32 bits	32 bits	32 bits
Processors	Intel StrongARM, Intel XScale	Intel XScale, Texas Instruments OMAP, Motorola Dragonball MX
Multimedia	Full support	need conversion for video
Expandability	great: SD-MMC, CF, CF-II,Microdrive	good SD-MMC, memory stick, CF
Wi-Fi	Yes	Yes
Bluetooth	Yes	Yes
PDA-phone integration	limited	good
Memory (RAM)	32-128 MB	16-64 MB

Multimedia:

Palm still lack video support because you should convert a video file to another proprietary format before using it and it doesn't allow streaming, while Windows Mobile 2003 on the other hand include Windows Media Player^TM for Pocket PC which allows streaming and viewing Windows Media formats.

Connectivity:

Both Palm and Windows Mobile 2003 have support for Bluetooth and Wi-Fi but Pocket PCs are the only devices to support Bluetooth and Wi-Fi in the same device like the HP 5000 series and the Toshiba E-750.
The difference in memory management between Pocket PC 2003 & Palm OS 5 is that Windows Mobile 2003 has an amount of memory that should be kept to be able to run the applications while on Palm OS there is no need to that: this is due to the multitasking capabilities of Microsoft OS.
What's new in Palm OS 5:

Improved GUI: support for higher resolutions i.e 320*320
Security: the OS support 128-bit encryption, SSL is also supported.
Multimedia : support for sound and video, this take full advantage of the new ARM processors
Wireless connectivity: 802.11b is supported , Bluetooth, GSM, CDMA.

[1]:Battery life varies from one device to another but generally speaking Palm OS has the best battery life followed by Symbian OS and then by Microsoft Pocket PC.
[2]:Symbian OS has software for the old OS of Symbian OS5 (Psion handhelds,i.e. Epoc Release 5) that can be ported

P.S :I tried to make this comparison the most objective possible one: I have no relations whith any companies mentionned above.