2011-12-01, 17:48 (This post was last modified: 2011-12-02, 05:14 by Orclas.)
Alright, because XBMC on XP lacks of CPU=>GPU decoding offload support pre Vista, which would then likely lead to CPU overload and plenty of stuttering. With Live/Linux, you get VDPAU support and 8400GS should be recent enough to support it in turn.
I have not tried XBMC on XP myself, but I know that playing full HD with VLC on XP is a disaster, stutters and pixelates badly, all while the fan reach jet speeds (on a P4 3.2 Ghz).
From there on I'll continue with another counter question: have you checked what the formally stated XBMC hardware requirements are, for example in the wiki?
HTPC: LibreELEC 7 on Shuttle XS35GTv2 & Raspberry Pi 3
NAS: NAS4Free 2x 3TB Raid1