Faulty keyboard i currently need to use the on-screen keyboard as the laptop keyboard will not function properly, what can i do to get it working again?

From your description I must assume that if all other keyboard functions and keys work properly then the keyboard is faulty. For the number keys to print the upper case characters shown on those keys requires a shift key to be depressed or stuck. If all other keys work properly, replace the keyboard. Otherwise look for a stuck shift key. I have found keyboards for sale on Ebay.

To determine if the keyboard or the keyboard controller is faulty, plug an USB keyboard into the USB port on your laptop. If all the keys are OK on the USB keyboard then the laptop's keyboard is faulty and needs to be replaced. If the USB keyboard also malfunctions then the keyboard controller chip on the motherboard is faulty, then the motherboard needs to be replaced, but this may not be a cost effective solution.
A replacement keyboard for your model laptop maybe available from this WEB site.Keyboard replacement, LCD screens for mobile phones, Ipods and computer equipment. http://www.yallstore.com/index.php?main_page=advanced_search_result&search_in_description=1&zenid=1lrjst3ncshlb4c7frn9bev3c3&keyword=keyboards

To determine if you need to replace the keyboard, connect an USB keyboard to your laptop and if the USB keyboard functions properly then you need to replace the laptop keyboard.
If the USB keyboard malfunctions too then the motherboard is faulty.
It may not be cost effective to replace the motherboard.

To determine if you need to replace the keyboard, connect an USB keyboard to your laptop and if the USB keyboard functions properly then you need to replace the laptop keyboard.
If the USB keyboard malfunctions too then the motherboard is faulty.
It may not be cost effective to replace the motherboard.

The keyboard maybe faulty.
Connect an external keyboard to youe laptop and if all the key work on this keyboard then most like the laptop keyboard is faulty.
If this external keyboard also malfunctions then the keyboard controller chip on the laptop motherboard is faulty and it would not be worth repairing as this is an old model laptop.

Replacing individual keys on some laptops can be a real problem, including finding just the one key you need. On toshiba's if the key has come off it's often because it has broken off, not just popped off. Also because you say the key un-jams when pushing another key it seems there may well be more than just the one key not functioning properly. From what you've described it does sound like you'll need a new keyboard.

The keyboard may be faulty and if so you need to replace it.
To determine if the keyboard is faulty or the keyboard controller chip is faulty, connect an USB keyboard to your laptop and if the keyboard functions correctly then the laptop's keyboard is faulty.
Replacement keyboard is available from this WEB site.
http://www.yallstore.com/index.php?main_page=advanced_search_result&search_in_description=1&zenid=1lrjst3ncshlb4c7frn9bev3c3&keyword=keyboards

To determine if the keyboard is faulty or the keyboard controller chip is faulty, connect an USB keyboard to your Acer. If the USB keyboard functions normally then keyboard is faulty then the keyboard needs to be replaced.

If the USB keyboard does not work properly the the keyboard chip on the motherboard is faulty and the motherboard needs replacing. This may not be cost effective and it may be better to get a new laptop.

Check out this WEB site for replacement keyboard.
http://www.yallstore.com/index.php?main_page=advanced_search_result&search_in_description=1&zenid=1lrjst3ncshlb4c7frn9bev3c3&keyword=keyboards

Keyboard is faulty I would say. Replace the keyboard.

The IBM error 301 POST code means the keyboard is not responding correctly.
You could have a stuck key, or the keyboard cable is faulty and not making proper electrical contact.
You could have a faulty keyboard controller.
You may have a faulty keyboard which may had some fluid spilt on the keys.
Try clean and reconnect the keyboard cable.
If this doesn't work try connecting an USB keyboard and see if this keyboard functions correctly.
If none of these work you have a motherboard problem. The Thinkpad 600 is a very old laptop and it would not be worth fixing. I suggest putting your money towards a new laptop.