I've had the iPAQ HP4150 for about 2yrs and I've been pretty happy with it. RAM is a bit on the low side with only 64mb for ROM and saved data, =(. But thats what the 2GB SD card is for! =). The 400mhz processor is good for everything, except heavy emulation, but I got an overclocking utlility, XCPUscalar and its setting pretty happy at 478mhz.
I don't use it as often as I would like, but carrying it plus my cellphone, keys and wallet, its just begging to get lost. Im pretty forgetful, so losing a $400 PDA (what i bought it for a while back) would kill me.
Anyway, I loaded it with TCMP player which supports a shit load more files than WMA9, like DIVX and OGG and shit like that. Then I went and got AIM. Get it from AOL UK, for some weird reason, the US version, you gotta pay. Also, I got pocketNES, GBAadvance and Morphgear for all my gaming emulations and all run really well. Kills battery though. Lastly, I bought a keyboard, but dont use it often at all. Lugging it arund is annoying and typing on a PDA isnt ideal, because the screen is so small.
The only major downside is that it seems to hang often. All it requires is a softreset aka reboot and it works fine. It only happens when i forget to close some programs and overload the puny 64mb and processor.
Anyway, I would highly recommend an HP iPAQ or the Dell Axim. The Dell seems to give more bang for the buck. Maybe a trip to cnet.com and other reviewing sites would also be help.