Gigabit Questions (aka how do I take advantage of what I already have)

Any wireless router should work and you only need one cable per hard wired computers. I have the ZyXEL x-550, very happy with it. Cheapr and looks like it'll will do the same things as the D-Link. You shouldn't need any special cables, most routers come with at least one cable.

yes any router will work, even a T10 base router since gigabit is backwards compatible, but you wont get any speed benifit since it would be limited to 10 magabit. Simmerly if you have a T10/100 base router you will be limited to 100 megabit.
You will need 1st a router that supports Gigabit lan, which is more expensive, and atleast Cat 5e cabling to use gigabit lan.
The cables will have to be standard, that is, non crossover cables and are pretty easy to find. if you are refering to the WRT54G, not 45G(as i dont think that there is a 45G model) then it will limit your speed to 100 megabit.
The issue of course is that it wont matter if your PC has Gigabit internet if all the rest of the equipment is 100 megabit. Wireless of course only runs at 54 Megabits, and so transfer of files between the laptop and PC will be at a maximum of 54 megabits regardless of gigabit. Ofcourse if you do get your HTPC, and it has gigabit then the files will transfer at Gigabit speeds.
Also, one thing you must remember is that the gigabit intranet will not speed up your internet connection. If you signed on for a 6 meg connection then the fastest down speed you will have is limited to 6 meg.
I'd say have a look on the Routers chart here on toms, they will help you by giving you information on the performance of the router, it will show the difference between a cheap and expensive router enough to help you make a decision. I've got a WRT54G rev. 2, which has really crap wireless throughput, even when the connection status is at 54 meg, it will transfer files wirelessly at only around 5 megabits, (around 500Kbs) which is really crap when you deal with big files.
I hope this info helps - and if it confused you more then helped you...a job well done on my part

Nope, that was great! I'll just buy a router that is at the high end of the lowest common denominator for my computers network interfaces, then.

Thanks!
-G