I was interested in the Averatec 3500 as a machine that seemingly would fit my needs perfectly. I need something portable for working at odd times when I get a few minutes, and also to store ideas and documents. I also need to have decent entertainment value, and the ability to create CDs. And then I need to have graphics tablet capability for my non-professional artwork and photo retouching hobby.

Of course I was surprised that Photoshop and others don't work.

I've done a little digging. Most tablet-capable programs use the Wintab32.dll interface. In more recent incarnations of pen-based computing, I discover that Wintab has been discarded in favor of wisptis.exe (Windows Ink Services). There is also a shift to HID-based devices exclusively.

I hear that the digitizer in the C3500 is a serial-based version. What I believe is that the Windows driver for the digitizer, as it technically should, is only hooked to Ink Services. However, for some reason applications like Photoshop are not recognizing the presence of a tablet on wisptis, if it is not Wacom. Then Photoshop looks for a Wintab-standard device and also does not find one.

I only have a Wacom tablet, and no tablet PC, so I cannot verify much of this.
However, I have found that UC Logic was very compliant in 2001 by supplying their serial tablet protocol to a Linux driver effort. Apparently all UC Logic tablets used the same protocol. I also discovered that the later Aiptek Hyperpen tablets used a protocol that was only two bytes different from the UC Logic protocol. Aiptek Hyperpen devices currently work in Photoshop. I would be interested to find out if the Aiptek devices use wintab or wisptis. There is also a currently working Aiptek Linux driver. It would be interesting to find out if that driver could be modified to work with the UC Logic protocol with minimal effort.

Another approach may be to somehow trick applications such as Photoshop into believing that a Wacom tablet is present. Obviously wisptis is working with the UC Logic digitizer; the disconnect is between the applications and wisptis. Wisptis should be providing generic tablet events regardless of what brand of tablet is installed. I suspect that if normal XP was installed on the Averatec, and the normal serial driver installed from UC Logic, that Photoshop pressure sensitivity would work through wintab. But if we can get Photoshop and other programs to realize that a wisptis-compliant tablet is actually there, we might get this to work. Perhaps it could be as simple as a registry setting.

Of course, Photoshop may never have been compliant with anything other than wintab. In that case, the Averatec driver is only compatible with wisptis, since the Windows applications work correctly. It may be that Averatec made their own wisptis compliant driver, and are not using the UC logic driver at all.

I don't think this is directly helpful to anyone, but I hope it might put someone on the right path. I'd definitely suggest investigating Aiptek and possibly asking UC Logic for some guidance.