I have a Micro Innovations infrared keyboard. It works with all PDA's that have an IR port. If you get a new PDA, just downoad a new driver for it and it'll work with that one too. It's inexpensive, small, very compatible, and quick. However, a Targus Stowaway is closer to full-size, and that makes it a lot easier to type.
Unfortunately they haven't made it compatible with Windows Mobile 2003 yet. They will soon though.
www.mi-products.com
Good luck!
By the way I'm thinking about buying an iPAQ from the 2200 series. Would you recommend it? My other choice is a 1935. Big difference - big decision.