There is no real "truth". The 8600 seems to be outperforming the 2600xt though in the latest benchmarks even with the newer drivers.http://www.elitebastards.com/cms/index.php?option=com_content&task=view&id=445&Itemid=27&limit=1&limitstart=3http://www.bit-tech.net/hardware/2007/08/14/radeon_hd_2600_xt_vs_geforce_8600_gt/1
Those are just a few places that did tests with the newer drivers. As you can see the 2600xt performs much better than the Tom's hardware charts suggest (with the old drivers). But, the two cards are about even now. Therefore, the choice is really yours depending on what is important to you and what software comes with the individual cards that you are looking at.
Cleeve, what about the 8600gt or 8600gts? These benchmarks seem to indicate that these cards outperform the 2600xt. I'm asking because I am actually considering these cards as well for an HTPC.