The Configuration dialog does not currently resize to fit its contents and is not wide enough.
As you can see in this image it's currently cutting off the Thumbnails tab (and anything that might be further to the right?) for me.

If it weren't for the wiki I'd never know that tab existed. Ctrl+Tab doesn't seem to cycle the tabs, the dialog can't be resized, and when I cheat and use AutoHotkey to resize the dialog itself the contents are still constrained by the grouping frame (at which point I gave up trying to check for other tabs).
I'm using the default Windows XP (SP2) style, with the silver color scheme, and normal font sizes. My display settings are for dual monitor:
Primary Monitor: Dell LCD: 1280x1024, 32bit Color, 60Hz refresh rate, Normal Size (96 DPI)
Secondary Monitor (on left): Dell Laptop: 1440x900, 32bit Color, 60Hz refresh rate, Normal Size (96 DPI)
It's a bit surprising that no one else is having the problem (or reporting it at least) since these settings are mostly default. Granted, it cuts off enough of the tab that you aren't suspecting anything is missing.
I know it's a tricky thing to solve, Firefox was, and could still be, plagued by it under certain themes, though for them if you use another program to resize the dialog you can find everything. Sorry I can't offer any advice on fixing it, aside from allowing the dialog to resized properly, but I'll gladly help debug changes.
XYplorer Beta Club