I currently use the smfgarage mod (http://www.smfgarage.com/) but am concerned that the developer hasn't been active on his own site for about a year and his site is full of spam, so am looking at removing it from my site. I'm not clued up with coding or how forum's work but I do install packages myself and also admin my own forum. I notice that the SMF Dynamic Directory says it can be used for a garagemod, is this likely to be the same as I have now, Would I gain anything by removing the mod I have and installing Dynamic Directory instead ? How easy would it be to set up ?

Well not as advanced as that mod. You can rename items (so they are called "Car" or "Vehicle") and you can also create custom fields (Model, Manufacturer, Kilometers...). That's how I setup one for a custom a few years ago.