Is there a way to limit the range of my wireless router? (internal settings etc.)

Some have a TX Power setting. This "turns down the volume" of the radio and limits the range that the signal can be picked up at.

Before I secured mine I folded down the antenna and sometimes covered it with something.

I would say most routers do or should mostly likely but it probably depends on what you have. Somewhere in router settings should have like Full Half 1/4 or 1/8 power output. Also reducing power doesn't always mean less throughput or slower speeds and does have its advantages.

But if that's not the case and no real option to do so ya could try maybe put metal objects or meshes etc around the router, certain spots or walls to stop signal from travelling further. :P

I wouldn't bother. If it's for security's sake go with a password.

yes, but the internal operating system that it has will not allow it, you would have to upgrade it to a different IOS.

It depends on the firmware. I think it's pre-Linux firmware and cannot be upgraded. With some hack firmware you can limit the wireless transmitter.

What router make and model are you using? Some have a built in function to limit the output power, this may also result in a slower connection to the router. If it does not have a setting to limit power, you may still be in luck, depening on the make and model you may be eligible to run Custom firmware like DDWRT, Tomato, FreeWRT, HyperWRT, HyperWRT Thibor, OpenWRT, Tarifa and X-Wrt and it can work on routers from many companies including but not limited to Linksys, Buffalo, Netgear, SMC, and more. Keep in mind that not all routers will run custom firmware so make sure yours is on the supported list.

http://www.decimation.com/markw/2007/10/02/dd-wrt-vs-tomato-winner-is-tomato/
http://forums.vr-zone.com/showthread.php?t=150144

Most new Wireless Routers have a power setting for the Radio. By changing the output power of the Radio on the router, you effectively reduce its range.

The broadcast strength is configurable on some models, but that's not always a good idea. Different PCs (actually their wifi cards) may be less sensitive and need the stronger signal to connect reliably. Also, different building materials, cordless phones, etc. can also introduce interference.

If this is for security you're better off using MAC address lists or a password.

What router do you have? Then we would be able to tell if the router has the capability to shorten its wireless range. We could also give you instructions on how to do it.