So, it sounds like you are attempting to run the external HDD off the laptop connected wirelessly to your your and then your network? If so, stop.
Hardwire only.
Most routers cap out around 20MB/sec in file transfer performance through USB connect hard drives. If that. A lot are in the low teens or high single digits (not sure on the N66R, but I don't it is terribly speedy). Most actualy computers or even cheap NAS can do significantly better than this. Even a 2006 laptop probably can, at least if it has a gigabit LAN port on it.
If not, you can probably get a PCMCIA gigabit card, or just a USB2 gigabit network adapter for it and plug it in to the switch/router to share files through the USB2 HDD connected to it.
Its going to be a lot faster than a wireless connection to the router and then to the rest of your devices or connecting the drive to the router itself. If you are connecting laptop to router wirelessly then to the device actually trying to access the file you are halving your wireless bandwidth because you have to make two wireless hops instead of one.
Never run a server wirelessly unless there is absolutely no choice (like someone is threatening your children at knife point to run it wirelessly, or else).
I have never run a server wirelessly. Actually I currently have the external 2TB USB HD plugged into one of the two USB ports on the Asus RT-N66R wireless N router. What I was doing before getting the wireless N router and a wireless adapter for my downstairs laptop was this:
Lenovo T60 laptop connected by ethernet cable to my Buffalo WHR-HP-G54 802.11b/g wireless router, the same Western Digital Elements 2TB USB external HD was plugged into one of that laptop's USB ports. That HD had the data that I wanted to be able to access from all of the machines on my network, along with data I was generating on a daily basis. The most important of this data I was backing up, more or less frequently. So, no, not two wireless connections.
Now, I've been testing speeds on the network. Before installing the Asus wireless N router it was taking around 70 seconds to download a 101MB file to my OTHER Lenovo T60 laptop, which was downstairs (the DSL modem and router are upstairs). Now, the same laptop in the same location, but now with a newly installed wireless N PCI Express adapter card, and with the wireless N router newly installed (and the HD supplying the data connected by USB directly to the router), is downloading this file in around 21 seconds on average. The downloads (I've downloaded this same 101MB file dozens of times to my two wirelessly connected laptops) are varying quite a bit in speed, for reason(s) that completely escape me. Everything is the same AFAIK, and a few seconds apart the download times can vary by almost a factor of 2.
I might do a lot better with a dedicated server of some kind rather than having a HD attached to the router. Speeds might be significantly better (I am inexperienced and don't know), and I might have better backup support. I need to work out a better system of guarding against data loss due to HD failure. What I've been doing is very unsystematic. I had one of my Western Digital Elements 2TB external USB HD's fail on me suddenly and without warning a couple of weeks ago. I don't even know exactly what was on it. The most critical of my data was backed up elsewhere, fortunately, but I've lost some stuff that wasn't. I started a thread in the Memory and Storage forum, and I'm going to try to recover some of the data on the drive, if possible. I need to get another, bigger, HD in order to try the steps that people recommended in an effort to recover data.
BTW, all my devices have gigabit ethernet, and all the wirelessly connected machines (my two laptops) have wireless N cards. That's not counting my Nokia Lumia 520 smartphone, the only device for which I'm using the 2.4ghz band on the router for its wifi.