On your Windows computer, if you already HotSync to Microsoft Outlook with your Treo (probably using "PocketMirror"), you can usually get away with also installing ActiveSync for Windows Mobile 2003 / Pocket PC 2002 devices, such as iPAQs. Then you can synchronize all your data from the Treo to Outlook, then do an ActiveSync to push the data from Outlook to your iPAQ. I find that conflicts between HotSync and ActiveSync are fairly rare under (at least) Windows 2000 and XP. There is some risk of data duplication problems and other weirdness, but it generally works.
Alternately, infrared beaming can work too for small chunks of data and files. On iPAQs with Windows Mobile 2003, you want to sent JPG and other stuff using "IrOBEX" which is the object exchange version of Infrared data beaming.
Symbian OS devices are typically more inclined to Bluetooth but such handsets still have IR ports too (usually). Beaming calendar events is often difficult, but simple contact records can be beamed back and forth with reasonable success. Memo notes are the most reliable to beam between units since it's just text without any special data field formatting.
Protectors
Cradles
