... Nice looking car! Never slam it into gear, that's gonna cost you a lot of money eventually.
There are a lot of threads about what you have to check out to make sure you have a healthy gearshift system, so start with the simple stuff first. This isn't an exhaustive list by the way.
This could be anything from low fluid or a clutch adjustment, to worn parts outside the transaxle (usually bushings) or at the last gasp, some parts inside the box. So start with making sure you have a gearbox full of fluid. Then there's the clutch.
If it's not fully releasing the clutch-disk when the pedal is completely depressed, it will be hard to shift into gear. If that's ok, are all of your shift-rod bushings in good shape and the shifter positioned right? How is reverse? Regardless a thorough inspection will tell you the story.
Dr. Evil has a whole set of instructions in this forum about how to do this. Do you have manuals (Haynes, Factory, etc)? They'll be required eventually if you're gonna do this and other things yourself. On this Evil has a really good batch of instructions in addition to a DVD set on a complete 914 transaxle rebuild that will lead you by the nose if you're mechanically inclined.
Good luck!