Slow/stuttering live TV any ideas?

[ThaClown]

MediaPortal Version: MediaPortal svn 11-25-2006 20-02 Rev11914
MediaPortal Skin: Steel two wide
Windows Version: Windows XP, sp2
CPU Type: AMD Athlon64 3200+
HDD: 320GB SATA2 8mb, Seagate
Memory: 1GB: 2x 512Mb DDR2 667MHz
Motherboard: ASRock ALive NF4G-DVI AM2
Motherboard Chipset: Asus Extreme AX300SE-X (Radeon x300SE)
Video Card: Asus Extreme AX300SE-X (Radeon x300SE)
Sound Card: Integrated
1. TV Card: Hauppage WinTV PVR
Satelite/CableTV Provider:
HTPC Case: Silverstone LC11 (black)
Cooling: St. AMD Athlon64 cooler
Power Supply: Silverstone 300W-SST-LC11
Remote: Microsoft MCE remote, MCE keyboard
TV: LG
TV - HTPC Connection: Composite

Hello all,

I recently finished my HTPC project, and i love it.
The only problem that I have is that when the live TV is turned on everything slows down alot.

Moving to the TV guide while the live TV is on takes a very long time (when live TV is turned off it is fast).
Also changing channels is slow.

Everything else is very fast, DVD movies, music, tv series, internet radio all works great.
So the only problem seems to be with the tv signal. (the signal itself is fine, my tv works fine as it is)

Is my problem in my video card (should I get a faster one?) or should I get certain codec's or drivers?

Edit: it works a bit faster with the lasted Hauppage drivers installed, but any tips would be welcome!

Any help would be great!

[ThaClown]

Anybody have any tips?