Check out snapstream or showshifter. Both work reasonably well, but both are products that must be purchased.
Neither one works nearly as good as Tivo though. The tv-guide implementation is non-existant or poor in both, you can't set up season passes to record your favorite shows, etc. Showshifter showed the most promise to me, but it's a few versions from being really cool. Do yourself a favor and just buy a Tivo - it's probably the single best electronics purchase I've made in the last couple of years.
This isn't a hot deal though - gonna get locked...