John,
I get the same error bobe4 gets on both old and new DVDs. As you suggested, I have confirmed that I have DirectX 9.0b using dxdiag. My DVDs will play fine using ATI's DVD player, but not WMP.
Media Center Registered 10.0.43 -- C:\Program Files\J River\Media Center\
Microsoft Windows XP 5.1 Service Pack 1 (Build 2600)
Intel Pentium 4 2538 MHz MMX / Memory: Total - 1048 MB, Free - 513 MB
Internet Explorer: 6.0.2800.1106 / ComCtl32.dll: 5.82 (xpsp1.020828-1920) / Shlwapi.dll: 6.00.2800.1276 / Shell32.dll: 6.00.2800.1233 (xpsp2.030604-1804) / wnaspi32.dll: 4.71 (0001) , ASPI for Win32 (95/NT) DLL, Copyright © 1989-2002 Adaptec, Inc. / Aspi32.sys: 4.71 (0001)
Ripping / Drive D: Copy mode:Normal CD Type:Auto Read speed:Max
Drive E: Copy mode:Normal CD Type:Auto Read speed:Max
Digital playback: Yes / Use YADB: Yes / Get cover art: Yes / Calc replay gain: Yes / Copy volume: 32767
Eject after ripping: No / Play sound after ripping: Yes Soundfile: C:\Program Files\Ahead\Nero\Trumpet1.wav
Burning / Drive D: YAMAHA CRW-F1E Addr: 1:0:0 Speed:44 MaxSpeed:44 BurnProof:Yes
Drive E: SONY DVD RW DRU-510A Addr: 1:1:0 Speed:24 MaxSpeed:24 BurnProof:Yes
Test mode: No / Eject after writing: No / Direct decoding: Yes / Write CD-Text: Yes
Use playback settings: No / Normalization: None