Will Creating a 2nd steam account work on the same computer / will i be able to play tf2 with the already downloaded version as an f2p on the new account, or will i have to download a 2nd verion of tf2 for the same computer?
The currently downloaded version of TF2 will do. You do not ostensibly need to download a different version for different accounts.
If so, i know my items would not be affected because of the cloud but would this be considered cheating towards VAC
No. Items are bound to accounts. Different accounts have different inventories and trading them between accounts involves being logged in with both Steam accounts at the same time.
would this be considered cheating towards VAC
We can't tell you. Steam probably has ways to know what you're up to, but so far has ostensibly done nothing about it.
how will i tell the difference between that and the Version i payed for years ago?
One has the Proof of Purchase, the other won't.
If you want to play on the same PC:
Yes. Steam should recognise that the game is already installed. Failing that (which definitely works on games newer to Steam, but I'm unsure about older games like TF2), copy the contents of your SteamApps folder to his. (see the SteamApps\username instructions below)
If you want to play on seperate PCs:
Yes. Open your SteamApps folder. This will be depend on your operating system and be:
C:\Program Files\Steam\SteamApps
for 32 bit (older) Windows systems,
C:\Program Files (x86)\Steam\SteamApps
for 64 bit (newer) Windows systems, and
/Users/<username>/Library/Application Support/Steam/SteamApps
for Mac OS X systems.
You will need to copy all files who's name begins with "source" or "team fortress 2" from that folder on your PC to the folder on your brother's PC. There is also a file called winui.gcf which you will need to copy in there also.
Then follow the instructions in the below heading.
SteamApps\username folder instructions
You will also need to copy the <your steam username>\team fortress 2 folder inside your SteamApps folder to SteamApps\<your brothers steam username>\team fortress 2. If there are any folders beginning with source or winui in there as well, you should copy those also. Apart from required files for the game itself, these folders contain configuration and downloaded maps.
Notes
If you miss any individual files then they will be downloaded when Steam launches the game.
These instructions will not work for Windows to Mac, or Mac to Windows.
Best Answer
Have you considered just buying or trading for one?
A Strange* Market Gardener hovers around $0.60 on the Steam Community Market.
Otherwise, you can trade item for item on sites like backpack.tf - most listings for the Market Gardener ask for two weapons/1 scrap metal in return (sometimes listed as '0.11 ref').
* 'Strange' weapons track kills but are otherwise identical to regular weapons