How to install directx 8 on windows 7 64 bit

Try DirectX 9 which is backward compatible to 8.
http://www.microsoft.com/download/en/details.aspx?displ...

Thank you for your very fast reply. Unfortunately I need DirectX8.1 for a specific software that I run on my computer, and this software only works with DirectX8.1 ...

And the software is?

Programs written for DX 8.1 will run under DX 9 just fine, provided the developers did their job and properly queried for the presence of features before invoking them. If not, all bets are off and you may get weird behavior.

TriSpace by GeoStru Software - a software for topography  

Thanks willard, I'll give it a try, at the moment a certain feature that needs DirectX doesn't work at all, so I have nothing to loose

Hope it works out. DX9 was the last release to maintain backward compatibility with previous versions, which is probably why Win7 dropped support for older versions. DX10 and beyond are stand alone releases, so if you have a DX10 program you can't get away with only having DX11 installed.

You can try running your topo software inside a virtual machine (e.g. VirtualBox). You will need also "old" Windows like XP, where you can install DirectX 8.1

Thank you so much for all your answers, I installed DX9 but didn't worked like it should, talked with the producer and they said they will fix this problem asap
All the best!