Framedrops/Stuttering while watching HD-TV

MediaPortal Version: 1.2.1.0
MediaPortal Skin: Xfade
Windows Version: Windows 7 32Bit
CPU Type: Intel E2180 2GHz DualC.
HDD: Samsung SATA2 1TB
Memory: 2 GB DDR2
Motherboard: Intel DG45 ID
Video Card: Onboard X4500HD
Video Card Driver: 15.​17.​11.​2202 (2010-08-31)
Sound Card: Intel® High-Definition-Audio (Onboard)
Sound Card AC3: optical out
Sound Card Driver: latest
1. TV Card: Tevii S660 USB
1. TV Card Type: DVB-S
1. TV Card Driver: January 2010
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec: Vid: FFDSHOW / TV: PDVD 9
MPEG2 Audio Codec: FFDSHOW (passthr.)
h.264 Video Codec: PDVD 9
Satelite/CableTV Provider: Astra 19.2°E
HTPC Case: ASUS P-P2-M2A690G
Cooling: Boxed
Power Supply: SUGO SG02B-F
Remote: Toshiba X10
TV: Toshiba LCD
TV - HTPC Connection: HDMI

Hi There,

since one week i'm able to watch HD TV Channels (HD Interlaced). Unfortunately im experiencing "lags" from time to time. The occur randomly every 2 or 10 seconds.
My CPU latency is about 20-30% while watching, so this shouldn't be the reason.
The TV is operating at 50Hz and in Mediaportal Dynamic refresh rate changing is enabled.
When i press Shift+1 i could see Framedrops when the stuttering appears and the Refresh Rate is below 50Hz (about 49,48 and some times 45).

Could it be, that my onboard graphics is not able to deal with the TV Stream properly? (allthough i don't have the problem while watching HD Movies from a videfile)
What i tried:
Changed the Codec (Tried Windows DTV and Power DVD 11)
Tried most recent drivers for my graphic card.
Turned automatic refresh rate changer off

Nothing helped so far. Any ideas?
If it could be graphic card: Any Commendations for a good Graphic Card for a HTPC?

Thanks in advance!

Hotkey

I'm pretty sure that your problem is your onboard x4500HD. I Had an onboard ATI HD4250 and was not able to play 1080i60 materials properly. Onboard graphic is only good for progressive materias IMHO.

Videocard recommandation : I have a geforce 420 GT with a small score of 562 here http://www.videocardbenchmark.net/high_end_gpus.html

I can play everything. I suggest that you choose a videocards that does 562+ scores.