Could it be that Win7 has a different activation code for cablecard than Vista? Hope that isn't the case for the final release, we'll be back in the OEM mess again.
XPS420: Quad, 4 Gig, 650/1Tx2 internal, eSata Tower
Dual ATI Cable Cards (SA-800 M) TAs
T-W W Valley (LA)--Win7
ATI Radeon HD3870 (DVI/HDMI)
2 XP, 1 Macintosh X (10.4.11), HP 280N extender, Linksys DMA2100, DMA2200
Promise Ns4300 Raid 5