I can vouch for IrDA working between an iMac G3 and an eMate 300, at least for package sending. It's not particularly flexible, but you can use IrDA Package Installer (http://jerome.vernet.pagesperso-orange.fr/Softs/IrDAPack.sit) by Jerome Vernet if you only want send packages to the Newton. You also need the IrDA Tool extension, which is a bit of pain to find again if you lose it. This only works under Mac OS 9 though. I can't say if it'll work on a powerbook, but it might be worth a try. Keep in mind that it needs a nice direct line without interference or wobble to get a clean transfer. It's not going to be incredibly easy and it's a bit of a pain. With some early versions of Mac OS X you can supposedly use NewtSync/nSync -- whichever it's actual name is -- (http://thenowhereman.com/hacks/newton/)

You can also check out these sites:

http://web.ukonline.co.uk/kieran.miller/newton/irda.html

http://communicrossings.com/html/newton/sloup.htm

http://www.archive.org/details/tucows_32991_EETransfer

On another point, what's really odd is this: NewtVNC (http://communicrossings.com/html/newton/vnc.htm)

and no it doesn't work terribly well, at least not with an eMate (too little memory for most cases it seems, even with the 4mb upgrade). I've tried it with different settings using my eMate with a wavelan wireless card.