Debugging the Linux kernel with JTAG

What are good debugging and development tools for a novice to use to get experience with Linux on a device with JTAG, such as one of those popular old Linksys routers? (perhaps using openwrt source as a starting point)

I'd like to use one that has hidden USB ports (like the T-mobile version of the wrt-54g) to make the printer logging output of another device accessible through the router web server cheaply and with minimal space/power requirements. The printer is fed serial data, as found with gas pump printers.