Sharp chisels are your friend
If the blade is tilting, there are a number of reasons....
One, the jigsaw 'jig'/guide isn't straight (some can lean up to 45 degree), make sure it is properly 0'd out.
Second, your not pushing down firmly enough and the saw is bouncing up and down causing the blade to wobble around.
Third, your using the wrong type of blade - the harder the material, the more teeth per inch you'll need, as using a standard wood blade on MDF will cause the blade to wobble since the teeth are too big and it'll try to cut too much material in one go.
Using a jigsaw is not exactly easy to begin with, since you need a strong grip and steady hand. You won't get a perfect circle with one, but they can do good curves. If your going to be making several holes, then you could make a single template/jig and then use a Router.
Of course, you can get large circle cutter bits for drills.... they like to wobble a bit and take a bit of time to cut through something and are bessed used with a drill press.... like the following....
http://www.woodcraft.com/Family/2000799/Circle-Cutters.aspx
A Router (woodworking kind - not the networking kind), is either a hand-held or table top - High speed (30k rpm), small bit, cutting tool, think of a dremel on steroids. The bits come in many shapes and sizes, so it can do decorative finishes, grooves, curves, etc. They're usually used in conjunction with guides and jigs, since they are very hard to control free-hand. Typically, you fit a small guide wheel above the Bit, press the Router down against the surface your cutting (with guides set), start it up and then push the guide wheel against the jig. The bench kind are used extensively for making decorative coving, Dado rails and skirting boards.
That looks like a CNC miller... can see the outline of the word CNC on the left side (though that could be a model reference). CNC (Computer Numerically Controlled) mill is a bit different from a router. They are automated milling machines that can use Router bits. You program in a cutting pattern, material, dimensions, etc, press start, and it'll cut out what you programmed in with the tool that's inserted. The bench top moves around as it cuts away (hence the rails on the side).
looking good but we need more pic
Not bad man!
Now that im looking at it I would suggest getting some stereo speaker grills to use over the fans on the intake (just for aestetics) Especially if you could bronze them out against a stain. Just an idea.
The holes are pretty good for your first time really doing this (which from reading the thread this is something you are relatively new at) So dont be shy about it! I know some framers who cut worse holes!
Be sure to rubber it up though... I am not kidding about that being a problem a few months down the line. Wood likes vibration.
Prep, stain, seal, post pics!
Good luck!