In builder-speak, what you want is "structured wiring". While packages vary, the general idea is that you get a star-shaped topology of Cat5 and either 75-ohm coax or RG-6 that all converges on some sort of wiring closet where you might install your DSL modem and Ethernet hub.

For what it's worth, I bought my first house "spec" (pre-built; I just walked in and bought it). This was valuable for a lot of reasons. My fiancée and I have been living there for a while and have begun to develop a "wishlist" of features we want in our next house. You'll never really know until you do it yourself. Some of the things on our wishlist:

- more storage (more closet space, plus a room where all the boxes and junk can go -- what other people would put in a basement, here you need to have a separate room, as any basement you might dig would immediately fill with water)

- more kitchen cabinetry with more work surface (we have tons of kitchen gear and nowhere enough space to put it all)

- a bigger gas range, suitable for using a restaurant-sized Chinese wok. This would require more BTUs than a standard range.

- a home theater room, purpose built for the task (perhaps using fancy acoustic damping wall materials)

- a three car garage

- ten foot ceilings with ceiling fans (my previous apartments had 8-foot ceilings while my current house has 10-foot ceilings -- it's amazing what a difference that extra headroom makes in the feel of the house)

Add that all up, and it's going to be a pricey house, especially if we get it custom built. That's why it's called a "dream house." But, at least I know what I want, which I didn't a few years ago.