I've got NwN2 gold + SoZ D2d on winXP
need Dx9.0c and .NET 2.0 ( 3.5 works )
To backup, just rename your MyDocs\\NwN2 folder (localvault and saves folders are important, so are Override and UI folders, modules, campaign, hak, music, portaits, etc. for custom content). idk, you can just rename the player folder there; however there shouldn't be anything special in the installation folders ( unless you put something in ). always have a look and don't take my words for it
yeh ... uninstall, update windows, use something like CCleaner for a quick registry check and more importantly a harddrive cleanup. Then defrag, install the game and one expansion at a time, loading and playing for a few minutes between each, just to get things to settle into place. After -all- that you'll probably have to manually update to v1.23.1765
There's a good link for patching stickied up in General forum, and i do any number of defrags during this process to keep things packed in nice.