My first post seems to have disappeared...
As a field test, you can try running your system in safe mode (without networking if possible) and see if the video still stutters, this would rule out some problems as antivirus could cause this issue as well.
Your system specs will be useful, but exactly how your playing the video will give the most benefit.
Are you streaming (Netflix, Hulu, YouTube, etc..), are you playing from disc (svcd, DVD, blue-ray), or are you playing a local file.
If your playing a file, what application are you using to view it (media player, i-tunes, VLC, etc..), and what format is the file (MPG, AVI, MKV, M4a, etc...)
This information along with your system specs should be enough information for someone to identify if your system has any weaknesses that need tended to, or suggest alternate methods of playback.
Its new pc which is way better then the dell i had here are stats of HP Vs dell
AMD Phenom(tm) II X2 511 Processor, 3400 Mhz, 2 Core(s), Vs Dell IntelCore 2 Duo 2.2 MHZ
5G DDR 3 ram vs 2G DDR 2
750 GB** 7200 RPM Vs 500 GB 7200RPM
Video ATI 3650 512 DDR2 Vs ATI 3650 512 DDR2
Power Supply 250 Vs 350
I was watching AVI's Or playing world of warcraft which played fine on dell but has issues with HP
Now i ordered
Antec High Current Gamer Series HCG-750 750W ATX12V v2.3 / EPS12V v2.91 SLI Certified CrossFire Certified 80 PLUS BRONZE Certified Active PFC Power Supply
AMD Phenom II X6 1090T Black Edition Thuban 3.2GHz 6 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Six-Core Desktop Processor
This should fix the prob but im still curious how the dell ran every thing much better when the HP has far superior stats the only difference is 100 watts in PSU and i was wondering if that would actually cause the Lag spikes in wow, Or the occasional freezes in watching AVI's with WMC for about 6 to 8 secs then fly by and catch up.