I am not all that familiar with how pcs handle ssd's, but you may need to activate trim support in windows 7.
Maybe this will help:
What your describing might be a symptom.
Have you tried running the SSD Optimizer included in the Intel SSD Toolbox? I believe the HP Media Center PC M8125x utilizes an Intel ICH8 storage controller so it should work.
Do you have benchmarks of before and after to provide objective performance differences?
Video and photo editing are CPU and RAM intensive. A SSD would provide some benefit if the application cache is on the SSD but a better CPU or more RAM would provide much more gains.
Did you make sure that your laptop runs in AHCI mode and not IDE?
The other thing you can check of is that your laptop supports 3gb sata 2. If your laptop doesn't support 3 gb sata 2 you might not get the high speed you'd expect.
Even with AHCI and 3gb sata I still don't see the performance advertised under Windows 7.
Also check out these threads: