I found this info at http://www.jacurutu.org.uk/category/11/blogid/1. It may help. I posted the main info below.
"...Unfortunately, Nisis's website (www.nisis.com) was non-existant (perhaps that's why Scan are selling the tablets cheap...). Fortunately, the Internet Archive has copies of them from their archived copy of the G3 drivers page (or try to download direct). Note that the drivers packaged as version 3.10 do enable the pen pressure control to work with Photoshop - other (earlier) versions I've tried don't.
For reference, the Nisis products appear to be re-badged Aiptek tablets, so their drivers should work. However, they only appear to have version 3.08 drivers, which didn't enable pen pressure control in Photoshop for me.
Finally, I ought to plug Adobe Forums. There's a few threads on there about Nisis, Aiptek and other branded tablets (which seem to be the same models), and the problems associated with them. Expect lots of comments about "you should have bought Wacom". It's clear that Wacom tablets are the most reliable, but they are several times the price, so I guess the Nisis G3 was worth a couple of late nights tracking down the right drivers to get it all working.
Now all I need to do is actually try using the tablet for photo editing! "
I did a little research and I also found this site which may offer a solution. http://list.driverguide.com/list/company1629/index.html. Hopefully the driver you want is there. Good luck.
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