Don't worry about HDR. Besides X1800 and 7800 series, nothing can run it well today. The card should last you quite a while. However, when games like Doom 3, Far Cry, COD2 and FEAR come out, they change the outlook on graphics. Doom3/Far Cry wave caused many upgrades and now COD2 and FEAR make the cards that played Doom3 and FarCry well look slow.
However, the majority of games still haven't passed Doom3 or Far Cry, nevermind the latest and greatest. Thus it'll be ok for 1-2 years as others have said for the majority of games. Of course there will 3-4 games like the ones I mentioned that will pummel X800XT just like they made 9800XT look slow during their time. Of course that doesn't mean 9800XT cannot handle the majority of games today at 1024x768. Oblivion and Unreal 3 are probably going to be the 2 games that'll tax your card the most in 2006.
Throw the X800XT into your primary rig. It's faster than 2x6600GTs.