I've been working on my programming portfolio, but I don't have anything presentable right now. I do have this old Star Fox-like railshooter demo I could show off. I attempted to emulate the gameplay, and I used the actual models from Star Fox Assault since I don't have the 3D modeling talent or the time. They were converted to OBJ files, and loaded by my code. I'd like to make a Windows build of this demo simply to demonstrate basic graphics and gameplay programming skills, but I'm almost certain this is copyright infringement. It's not meant to be used in a commercial project, but it is meant to be used in a portfolio. Since I'm using a commercial game's models, is there any way I can use them, or should I resort to programmer art?

If this isn't possible, could I use free models obtained from places like BlendSwap or even TurboSquid as long as I give permission? Also, what are the grounds for font files? Some artists grant personal use. Would a portfolio fall under personal use, and not commercial use?

Using Ripped models (or any content you do not have the rights too) is Copyright Infringement.

Assuming you are creating this portfolio to get hired, some employers may not care/notice that you are using illegally aquired assets, and some most certainly will notice and will care, and will disqualify you from consideration right then and there (Making them aware of your illegal activities is a big nono, especially when you are blantly flaunting them (by using illegally aquired assets)).

As such, there is a plethora of free content you can use legally (especially as its for non-commercial use), so there is really no reason too. Just check the license of the asset (BlendSwap and TurboSquid both display it somewhere) and make sure you are able to use it for non-commercial use. Most licenses require attribution, and even if not, its definately a good idea to leave a caption with sources for content wherever you display said content.

As long as you have no ads or any way to generate revenue, a portfolio will fall under non-commercial use.

Also, what are the grounds for font files?

The issue is less clear if you were using these on your private machine and showing them on your laptop (as opposed to say, distributing the demo on your website which would be copyright infringement). In some countries even copying data on your own computer is copyright infringement unless explicitly allowed, but even there, that's on the same level as being illegal to copy music from a CD you legally bought to your computer or mp3 player.

If showing them on your own laptop, I don't see it being a bad thing to explain that you used models from a game you bought for learning purposes. You're being interviewed by developers, not lawyers, who should be more interested in your skills rather than a debate on when or whether EULAs are legally enforceable.

"If this isn't possible, could I use free models obtained from places like BlendSwap or even TurboSquid as long as I give permission?"

"free" can mean many things - check what the licence says. Another good place to check is opengameart.org (where everything is under Free/Open licences, meaning you can using things even commercially, but you must abide by what the licences say).

is there any way I can use them, or should I resort to programmer art?

You can get a license for them. That's likely to be non-trivial, so you should programmer art. You are correct that using these ripped assets constitutes copyright infringement (and possibly infringement of other forms of intellectual property, depending). However in addition to that you need to consider what such a presentation says about you, and how potential employers might take that.

Everybody who sees your portfolio will react differently, of course, but for my part I was always very turned off by a portfolio that included IP infringement. Programmer art I can understand, because I am a horrible artists as well and I don't expect pretty art from a programmer candidate. I do expect -- if not a basic understanding of IP law, some basic respect for the ideal that somebody else put time and effort into creating those assets and you're using them to promote yourself (because that's what you are doing) is rather unprofessional and rude.

So use programmer art or ensure you have a proper license to the assets in question (things you acquire from TurboSquid typically will be licensed accordingly).