I'm trying to run a valid download to update a soft synth by Steinberg called 'Halion Sonic'. Its extension is .msp. When I tried to execute it my PhotoPlus program opened (?!?!) and of course couldn't 'see' it. I've been into the Windows 'associate with' window but don't know what to associate it with. Ideally, I don't it associating with anything - I just want it to run. 
My Computer
At a glance
Windows 7 64 bit Home SP1Intel Sandy-bridge i7 3.4GHz, 4 cores, 8 threads14GBHD5450 ATI dual output silent cooling
- Computer Manufacturer/Model Number
- DARC (DirectResolutions, UK)
- OS
- Windows 7 64 bit Home SP1
- CPU
- Intel Sandy-bridge i7 3.4GHz, 4 cores, 8 threads
- Motherboard
- Gigabyte P67
- Memory
- 14GB
- Graphics Card(s)
- HD5450 ATI dual output silent cooling
- Sound Card
- Focusrite Saffire Pro 14
- Monitor(s) Displays
- Samsung 27"
- Screen Resolution
- 1920 x 1200
- Hard Drives
- 1TB OS drive
1TB Audio drive
1TB Audio drive
- PSU
- Zalman ZM600
- Case
- DARC Custom
- Cooling
- Fans front and back
- Keyboard
- Logitech
- Mouse
- MS Optical
- Internet Speed
- ADSL