Best Setup Suggestions

I've got what's probably a rhetorical question, but that's why I've posted it here.

I'm moving into my new house next week and I'm trying to figure out the best setup that's still relatively cheap. I basically have two zones that need access, the office and the living room.

Office
Desktop PC
XBOX 360

Living Room
Original Xbox running XBMC (effectively a Media Center PC)
Roku Netflix Player
Wii
Laptop (wireless)

Currently, I have two Linksys WRT54GS Wireless Routers with one running DD-WRT firmware in client mode from the office which allows the XBOX 360 a wireless connection to the living room. The Desktop has a wireless card, so it's not plugged into that router. I assume the gaming lag I experience is from two sources: a wireless connection and a DSL Internet connection that gets around 900k down/ 375k up (DSL reports Flash test results). The worst is when the lady is streaming Netflix from the Roku.

The XBMC Xbox streams music and videos from the Desktop PC. In my previous place, I had the whole system hardwired and had no problem streaming media. Now it can't barely load my music folder, and videos take around 30 seconds to cache. I assume this to also be due to the fact it's now set up wirelessly. That's really the only change.

In the new place, the two zones will be on opposite sides of adjacent rooms. The office is garden-level and the living room is on the ground floor, with a crawlspace underneath. I assume the best way to get this connected would be to hardwire the two routers together through the crawlspace. I could get some powerline networking adapters, but they're still relatively expensive ($120/pr) and I've heard questionable reviews. I'm probably going to drop a modified firmware onto the router in the living room so I can limit the bandwidth the lady gets for Netflix. I'm under contract with my ISP through January, at which point I plan to switch to cable internet. Until then, I'm guessing this is probably the best way to go, but that's why I post here.

Suggestions?