Home networking - advice sought

It occurred to me over the winter break that I have cobbled together a rather ridiculous mess. I have a total of 14 devices connected (mostly via ethernet, some via wifi) to our home network, and I'm betting that the use of hand-me-down equipment is creating packet bottlenecks that I could easily eliminate. I just don't know how to diagnose the bottlenecks (if they exist) and how to benchmark whether the current setup is sub-par.

Here's the current state of affairs:

• Room 1: I have a Netgear 4 port switch (I believe it's model FS105), into which my Sonos 90, PS3 and TiVo Series 3 are all plugged in. The Netgear is plugged into the CAT5 jack in the wall, using the existing home wiring to connect to my D-Link (DIR-625) router in the upstairs bedroom closet.
• Room 2: A Sonos 120 is wirelessly connected to the D-Link upstairs.
• Room 3: an Epson printer and two Windows desktop PCs are plugged into an older Linksys wireless router (where I've disabled the wireless antenna and am using it solely for the ethernet hub capability). A TiVo (series 2) is connected via 802.11g to the D-Link in the bedroom. The Wii is also connected via wifi to the D-Link in the bedroom.
• Room 4: TiVo HD is connected via ethernet into the wall jack, which is connected to the D-Link router in the bedroom closet. In the closet, the other Sonos 120 is connected via Ethernet to the D-Link router. The D-Link is connected to the Comcast cable modem.
• Both my wife's laptop and mine connect primarily via wifi to the network (she's on WinXP, I'm on a MacBook Pro).

I'm using WPA to secure the wireless. One of the wired connections actually terminates in the Sonos in the bedroom closet, don't recall which. (The Sonos has an additional ethernet ports to serve as a hub, specs on their site say "2-port switch (10/100Mbps, auto MDI/MDIX) allows Ethernet devices to connect through SonosNet".)

So... how badly am I slowing things down? What's the best resource for doing this right?