I doubt 2.6 will run well in Win 8. GIMP 2.6 was out LONG BEFORE Windows 8 - it was certainly never intended to work on Windows 8, since it didn't exist when GIMP 2.6 was developed. It's now out-dated. You might be able to get it to work in some sort of compatablity mode, but I would expect problems/glitches. Plus 2.6 was never that stable to begin with. Why do you think you need an outdated version of GIMP? You appear to have been given quite a bit of disinformation about the newest version (2.8) - I don't know who is telling you that crap, but crap it is!!!
GIMP 2.8 is the newest version - it runs in XP SP3, Vista, Win 7 and Win 8, Mac OSX, and Linux - it's the most stable version of GIMP yet. Only get it here: http://www.gimp.org - I use it all the time, It is not buggy at all, it's never crashed once, and it has no "superflous buttons" - GIMPs interface is fully customizable, always has been. The interface on 2.8 is vastly improved too - it has a new single window mode, more advanced brush dynamics, smoother editing (less banding) due to the new GEGL capabilites.
Relying on third party opinions on GIMP 2.8 from random people on the interent is a bit dumb. Anyone and everyone (including computer illiterates, morons, haters, and wacos) can get their hands on GIMP, since it's free. Tens of thousands try it, have no idea how to use it (it is complex software), and conclude it's therefore "no good". And I agree with them, it's no good for people like them. They need some simple software for their simple minds, and GIMP is definitely not simple.
It might be best if you were to seek for the opinions of people who actually use the software on a day to day basis - people who know how to use it.
BTW, There's only one thing you need to be wary about with 2.8, how you export file formats other than GIMP XCF has been changed. Now you need to use the new File > Export command instead of the old File > Save As command. Save and Save As in the new GIMP are now only reserved for saving XCF files.
If you still insist on trying out an older version of GIMP, that oldapps website is not a safe place to download old versions of GIMP. You want the official Windows sourceforge project here: http://gimp-win.sourceforge.net/old.html
Installing an old version won't do your computer any harm, if it doesn't work, just uninstall it.