Thanks to the little step-by-step guide from Vladimir7 (to be followed rigourously especially for the NFS server configuration part which will help prevent empty NFS folder on WDTV) and combining different things (thanks to wiki.wdtv.org,
b-rad.cc/wdlxtv), I'm now able to stream all my medias (music, photos, movies HD or not) wirelessly from my PC to the WDTV without almost no hiccups. This is my configuration :
Hardware:
PC Intel Core 2 Duo running Windows XP Pro
D-Link Router DIR-655
D-Link Wireless USB Adapter DWA-640
WDHDTV naturally
Software:
NFS Server from Windows Services For Unix 3.5
1.02.07_B-RAD.CC_WDLXTV-0.5.3.2.zip
wireless-mod-0.3-sebmod.zip