Thanks to everyone in this thread that helped me to decide on the hardware I needed for my new NAS.  I got the hardware last week, and had some fun on Friday setting it all up.  However, there's a few outstanding issues, which I'm hoping you might be able to with.

To catch people up, I ended up going with a QNAP TS-112 NAS, with a single WD Caviar Green 2TB HDD, and the TP-Link WR1043ND router.  The router is designed to replace the wireless function on my existing Linksys WAG54GP2 modem/router, which has been causing problems with our VOIP setup from Xnet, and to provide gigabit routing to the NAS.  We have two computers connecting via wireless (both with 802.11n), an iPhone 4 and 4S, and an iPad 1st gen.

When I setup the TP-Link, I figured that I would need to disable the routing functions of the Linksys, so I changed the mdoe from RFC2564 (or something like that) to bridge mode only.  However, that didn't work.  Bizarrely, I could only get it to work if I left the Linksys exactly as it was configured when it was working as a modem/router.  This meant that I had the Linksys acting as a modem/router, and the TP-Link connecting its WAN port to a LAN port on the Linksys.  It worked, in so far as I could access the internet and the LAN from all of my computers and devices (wirelessly through the TP-Link - I disabled the wireless mode of the Linksys).  My first question is whether the setup is correct, or whether I should have the Linksys setup differently.

The second issue relates to wireless speeds.  After setting up the new router and NAS, I had a go at transferring a 2GB file over the wireless.  The best speed I got in the real world was 5MB/s, and that was with the laptop sitting right next to the router's antennae.  I tried with an ethernet cable, and got speeds of 37MB/s.  The first question here is whether the ethernet speed is normal, or whether it should be higher?  By my calculation it works out to be about 300mbps, and given that the router and the NAS are both gigabit, I expected it to be higher.  The second question here is about wireless speeds.  I set the router to connect via 802.11n only, to avoid any downgrading by an errant 802.11g device, and the speeds still didn't rise about 5MB/s in the real world.  I tried some tests using LAN Speed Test, with both ethernet and wireless.  Under ethernet, I got speeds of about 350mbps, and under wireless about 50mbps.  So the test results roughly match the real world test results.  But I would have expected the wireless to be much higher if they were connecting using 802.11n.  Have I misunderstood something, or is there another setting I need to change?

To complicate matters, the whole network started exhibiting some bizarre behaviour this morning, and I wasn't able to connect via wifi at all on any of my devices, despite returning all the settings to the original state last night.  After resetting both the modem and the router, it still wouldn't connect, but would over ethernet.  So that's something else I'll have to diagnose tonight.  But I'm hoping some of you will have some suggestions for my questions about configuration and wifi speed.