Here is what does and doesn't work for the PowerPro IV:28/IV-28A:

Built-in 10/100 network works 
USB 2.0 works (USB1.1 device tested)
CD burning works 
DVD movie playback works (Xine must be updated with DVD support)
Built-in Audio works (headphone out and mic in tested)
Floppy drive (optional) works
Parallel port works
1394 Firewire works
Built-in 802.11b works !
ACPI somewhat (suspend to disk available on command or when closing lid - not enabled by default; Battery info is not reported correctly. ACPI conflicts with the modem and must be disabled for that)
PCMCIA controller works
v.90 modem
(winmodem)
Does not work (The modem dials and sound can be heard. However, we never achieved a connection. It apparantly uses a Conexant chip)
Sony MemoryStick slot Does not work (Device does not appear in lspci)
FiR/IrDA Infrared untested