The Olimex ARM JTAG clone is well known as there are many schematics in the internet available. Circuits is very simple and seems to be reliable. This adapter can be also set up to work with WinARM tools: ocdremote and gdb/Insight-gdb. In the circuit there is a critical part that needs to be considered – 74HC244 buffer IC. Family of HC support less than 4.8V if powered with 3.3V. But reality shows that Parallel port voltage usually is lower than 5V, so HC will fit. But of course it is better to measure the HIGH state of parallel port pins. To be more sure HC should be replaced by 74LVP244 or 74LPT244. These chips support 5.5V in entry with 3.3V supply but sometimes they are hard to find in the market.
Usually one solution of debugging is to run compiled code on PC simulator. You can download a limited version of instruction set simulator from Hitex for free. Of course better simulators aren’t for free. More advanced simulators you can purchase at Keil. More advanced I mean that there is ability to simulate peripherals by additional scripting and so on. But again, simulators re virtual tools and usually it is hard to simulate real world events. Once you face this problem, you are going to switch to real world simulation using JTAG.