Hacking routers is a fun and worthwhile past-time. One of the simplest hacks is to install the DD-WRT firmware on your router.
DD-WRT is a highly configurable open source linux based operating system you can easily install to get increased functionality out of an old router.
From there, configurations can be either complex or simple. However, even at the default level, DD-WRT provides more security than your average Netgear router straight out-of-the-box.
Is your router supported by DD-WRT? Find out over at the DD-WRT wiki page.