When I install the Windows Mobile 6 Standard SDK Refresh I get the error:
Not Installed: Visual Studio 2005 SP1 or Later
I
I don't know if there's any workaround for this particular case, but Visual Studio and its add-ons are in general notorious for requiring exact versions of all dependencies, leading to conflicts that often make it impossible to install the versions you want of everything.
Personally I keep a virtual machine for each Visual Studio environment to keep the dependencies happy. You might benefit from running either VS2010 or VS2005 or both in a VirtualBox/VirtualPC/VMware.